Why do the enemies have finite aggro ranges?

Question

Edit: (September 18 2021) So far there are are many good answers that address why a group of guard monsters or unaffiliated group of humans might have a finite aggro range.

However these answers are unsatisfactory, because they do not attempt to explain the example where the heroes can attack a castle and clear it room-by-room, without having to fight all the guards at once.

In this case the guard groups are affiliated with each other. In reality I would expect a command structure with a plan for what to do in case they are attacked. I would not expect them to stand idle while the heroes murder their colleagues at the other end of the room, and wait for their turn at the slaughter.

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Often in video games (and to a lesser extent tabletop games) the enemies have finite aggro ranges. That means for example, even on a featureless flat plain, the Man-Eating Troll will ignore the heroes before they come within 60 feet. Only then does the troll attack and try to man-eat the heroes. If the heroes later retreat to outside the aggro range, the troll forgets they exist and returns to its original position or patrol route.

In practice this is to allow adventures where the heroes take on a much larger force by fighting them in small groups. For example to take over a castle, first they fight the soldiers at the Gate House. Then they fight the soldiers at Ramparts East. Then Ramparts West. Then the Guard Tower. . . and so on until every room of the castle is cleared separately, and the final encounter is with the king and his royal bodyguards.

This requires great suspension of disbelief, since attacking the gatehouse should realistically alert all the troops in the castle, either by raising the alarm or the noise of fighting drawing soldiers from elsewhere. Soon our heroes will find all the soldiers in the castle on top of them.

An even sillier example -- in large rooms our heroes can often fight and kill the Manticores at the entrance without drawing the attention of the Basilisks at the exit. Even though the heroes can see the Basilisks, the monsters are either unaware or indifferent to the heroes, since their aggro range is smaller than the room.

From a world-building perspective, what would explain this strange behaviour? The goal is to keep as much of this strange video-game features while making as few changes to the real world as possible.

For example we could declare that all the monsters and enemy troops are in fact golems that are powered by crystals hidden below the floor. They simply fall down dead if they stray too far from their spawn points. This also explains why they fight to the death. They are non sentient and so lack a self-preservation instinct.

However this solution falls down in that (a) it is is a radical departure from the real world and (b) it does not explain why the golems are so common, when they are less effective at defending the castle than living beings, and presumably more difficult to acquire.

So what is the optimal tradeoff between modifying the real world as little as possible to produce as much strange video-game logic as possible?

Answer 1

So, drawing on a few real-world examples

Too much hassle

It is just too much hassle to pursue the adventurers past a certain point. If you never gave up doing something because you realized it would be too much effort for too little reward, you may throw a stone at this argument. However, this is a very successful tactic for price increase, especially in services. Do a minor stealthy price increase in your service - most customers will not do anything because the hassle of changing service providers or calling customer service to haggle / take the charge out of the bill is too much hassle

Violation of orders

A slightly more specific version of the possibility above: the enemy character is posted to guard a post or patrol a route. They have orders to not get further from X meters from the post of the route without authorization of a superior. They see the group and engage in combat. The group of adventurers retreat past the point they're authorized to go. So the enemy decides to not pursue them further because it doesn't justify violating their orders or asking authorization from their superior.

Bystander effect

Related to the fighting happening in the same room. It is a well-documented phenomenon in humans, it could very well happen with monsters. Or maybe getting rid of the pesky manticores is exactly what the basilisks wanted but lacked firepower to do...

Limited aggro range = limited sensory range

Animals can see, hear, smell and feel things we can't. We can see, hear, smell and feel things some animals can't. Maybe your monsters have limited range and they literally don't perceive the fight happening in the other side of the room

Answer 2

In real life aggression is always justified by removal of a perceived threat, with saving energies being always tell priority.

Bees and wasps won't chase you for miles and miles, Canadian geese will desist from hitting you, and so on and so on, as soon as you don't represent a threat anymore.

And even in human behavior, there is always a chance that an attack on a side is a lure to leave another side uncovered or less covered.

Answer 3

The perceptual range of these enemies is limited.

source

Last winter I was walking my dog around the block. It was night. On the street over she got scared. She wanted to turn around. She set her feet. She has been down this street thousands of times.

I looked down the street. Nothing and no-one. No sounds. No trucks.

And scared dog. We turned around. There was no reason we had to go down that street. I know she can hear things and smell things that I can't. What if she was right?

The next day that street was fine for walking.

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My perceptual range is not great; at least not compared to a dog. Your video game enemies are like me except less good looking. They just cannot see or hear very well, and have essentially no sense of smell. The palace guards have a lifetime of rock concerts and jackhammer use dulling their hearing, plus they went lake swimming last weekend and their ears are still plugged. Their vision is not great either, between the syphilis and the shrooms. Your assorted bugbears and black puddings are likewise limited in perceptual range.

Answer 4

Finite aggro ranges could be considered a natural extension of the end-stage development of an evil fascist organisation.

Isolation and compartmentalisation of wider society is the first step towards instigating a fascist dictatorship. The unity of the people must first be undermined and replaced with feelings of distrust in one another, fear of the unknown and faith in authority. This pattern persists within the evil organisation by design so that the workers never unify and rebel against their evil overlords, and instead continue to obey orders without question.

Compartmentalisation is a key feature of most modern security and information policies. The effect of compartmentalisation is that each evil NPC peon is assigned an exclusive area which they are responsible for defending, Eg. a 30 yard zone, outside of which they stop chasing you and ignore any threats. They are not rewarded for addressing threats outside of their designated zone and may be punished personally for a security breach within their remit.

There may be another 30 yard zone at the far end of the room which is currently being raided by adventurers, but that is effectively another department within the organisation and so it doesn't matter in the slightest to our peon who is occupied within his own department. He could run to help his colleagues but there is no incentive to do so and he will be in trouble with his superiors if he leaves his block and it is subsequently invaded. - Remember the leaders of this evil organisation are themselves entirely selfish and myopic in their focus, and this influences workplace culture accordingly.

The Boss mob of the dungeon is bound in a similar way to their lower peons. They could instruct all their underlings to charge together and attack the adventurers at the entrance of the dungeon the moment they step inside, but they would be disregarding the security policy handed down from their own superiors. If the Boss mob leaves his zone, or instructs his underlings to do so in contradiction to HR and security policies, he would be held personally responsible for the outcome of events. Fear of the unknown and obedience to their superiors keeps them in line.

It is also worth noting that members of any organisation need to feel like they are doing the right thing; that they are 'the good guys'. If the average peon knew the extent of their corporations activities in the outside world they would realise that they are not, in actuality, the entirely righteous and benevolent philanthropists which they claim to be. Compartmentalisation within the organisation means that each peon knows only what he needs to do his job. Therefore if he is killed or captured it is unlikely that he will divulge any key items or information to the adventurers. For the same reason the Boss will not engage the adventurers prematurely - if he should be killed then he is likely to divulge helpful items or info to the party, and this is a risk that should not be taken except when absolutely necessary (i.e. when a threat has entered their delineated 30-yard aggro zone.)

Answer 5

The monsters have reasons and purpose

Some of the monsters are probably guards, and don't want to stray too far from what they're guarding, because that would leave it unguarded.

Similarly, some of the monsters might be hanging around their home/nest/property, and are only concerned with the adventurer, because they see him as a thread to that.

Perhaps some of the monsters have tasks to accomplish where they are, and are therefore reluctant to drop that task just to chase adventurers.

Perhaps some of them are just lazy, and don't want to run too far, because then they'd have to walk back.

Think of all the moments in your own very real day and how difficult it would really be for someone to get you to drop what you're doing and chase them in any of those moments.

If you want to make the reasons for a limited aggro range realistic, then make them diverse and varied, and think of a different realistic reason for each case. Don't assume that antagonizing adventurers is the monsters' whole reason for being.

Answer 6

Biologically hardwired

Humans quickly attribute human emotions and logic to non-human creatures and even things. This is called anthropomorphism. Yet most don't work like us. We can make them not working like us to an extreme.

Some examples of different behaviour is plenty. We see showing teeth often as smiling, while for many creatures it's aggression. A woman wouldn't eat their husband after sex, while some do (sometimes) for immediate nutrition and better survival. We see others get hurt and want to assist or do something with the threat, while some creatures just run or do simply nothing about it.

We think creatures would immediately be get aggressive when they spot us. But that is human logic. Creatures 'guarding' caves can just have loyalty to these few at the entrance, recognising them as important. The rest simply isn't. The heroes are also a special case. They are unusually strong and skilled, but this isn't recognised by the creatures. Even if the creatures a little ways away are attacked and killed, they are secure in their own strength. They have been strong compared to all other threats so far, so their own group doesn't see the danger. They stay put at their fruitful location.

If the heroes run away out of their aggro range, they see that as a win. They lick their wounds and possibly mourn their dead. They only recognise their win, seeing their victory as proof they don't need to do anything when the heroes are closing in on their aggro range again.

You can use these behaviours in both smart as well as dumb creatures. Culture, religion, instincts and more can make them act the same, or completely different. It just depends on your requirements. Just like in real life you see differences and similarities even within the same creatures. From spawn rate → some same fish with or without many predators can make them spawn more, smaller and quicker, or less, slower and bigger. To size and loyalty to a group → size of a pride of lions and how well they stay together.

The guards can see the attack as a small group, which doesn't need immediate attention. It isn't a siege or something. Besides, their military structure tells them to guard that wall and not to rush down. The small group should get cleaned up by their peers, or get stopped when they get to stronger guards deeper in the palace. Their honor even prevents them. It is the fight of those guards. Only if the enemy gets on their territory they need to rush and defend their piece.

Answer 7

My first thought was a variation of your "Robots with energy crystals below the floor" thing, though one that fits better into a "natural" fantasy world:

Magical creatures need magic, which flows in leylines or gathers in pools

These monsters are stronger than animals in our world would be. This obviously requires them to have more energy available. They also never eat (unless they eat a hero), so where do they get the energy to exist and breathe fire? It must be magic!

Now some worlds have magic just everywhere, in a diffuse field that anyone can access everywhere. That would allow magical creatures to roam freely. In your world however, magic either flows in leylines or acts like a liquid that collects in the deepest parts of... well, magic doesn't really flow over the ground. It gathers in divots of the etherical field (or somesuch babble).

A monster can't exist for a long time outside of such a pool of magic / away from a crossing of leylines. Anything outside its personal pool (or that of its pack) is not a threat unless it moves close enough to be seen as interested in this pool.

Hero walks past the monster with enough distance between them? Oh, he doesn't want to steal my magic pool that I need to live. Why should I leave my pool, risking that someone else takes it away from me, to chase down someone who is no threat to me?

Hero comes too close though? Clearly this creature wants my magic pool, otherwise it would not come close to my fangs, claws and fire breath. My only options are to fight, kill it and keep my life-sustaining pool, or be driven out of my pool and starve to death if I don't find another one soon enough!

Basically, the monsters have no drive to chase the hero for food because they're sustained by magic. And they don't see him as a threat unless he seems to be interested in their personal small location where magic is strong.

Answer 8

Westworld style

Just replace:

For example we could declare that all the monsters and enemy troops are in fact golems that are powered by crystals hidden below the floor.

With:

The enemies are robots, built for the pleasure of the patrons who like this kind of fight.

The gods decreed so

There is a very popular webcomic called The Order of the Stick, which is all based in Dungeons and Dragons. In this epic story, the gods created monsters for the sole purpose of serving as XP sources for heroes. The sentient monsters do not like this fact one bit, but even though they have free will, they must still abide by the rules of the world. It's kinda like the laws of physics for them.

Answer 9

Monsters

With monsters, it's seems sensible that you could treat these like you would animals, just ones with extra powers and maybe slightly more intelligence.

Take a lumbering man-eating troll posted at a cave. You could argue that it is unlikely to run far towards humans it sees from a great distance. Why would it? The humans can almost certainly see it and are almost certainly faster. Surely that would be wasting energy catching prey that would easily get away if it wanted. Why do that when there is a ready food supply that seems very content in approaching its home quite willingly?

Further, if this location were indeed its "territory", it might not want to venture far for fear of its claim on that territory being threatened by some other creature (human, troll or otherwise), even without explicitly being given orders to guard anything.

For a mixture of monsters in a location, there may be some reason that it's beneficial for them to coexist without them necessarily having any kind of allegiance or devotedness to each other. So if you attack a Manticore, there is no real reason that a Basilisk feels the need to intervene as long as you don't enter its own personal space.

Humans

Personally I think this one is harder to answer. It could be that their masters foster a certain mentality that causes this.

Maybe they have very strict instructions and they're frightened to leave a limited range for any reason for fear of reprisal, instead training themselves to ignore anything going on in other parts of the castle that doesn't concern them. Perhaps infighting between guards or run ins between human guards and the monstrous ones is commonplace and thus they don't jump to the conclusion that the commotion is the result of an intruder until they see otherwise, ignoring it because they're more focused on themselves. And speaking of being focused on oneself, they may be far from fanatical over aiding their masters and take a "That over there's not my job, I'll only get involved if I have to" approach to their duties.

Answer 10

A part of it can be territoriality - why does the Manticores not attack the Basilisks? Because they have established which side of the room is for which species. Plenty of animals exhibit this behaviour pattern which informs both intraspecies (this area, and any females or prey in it, is mine, so don't come here unless you want to fight me for it) or interspecies (detecting a dangerous predator by scent markings or spoor) activities.

For the mixes of monsters to coexist closely packed in dungeons or whatever some similar stand off is needed. Of course that leaves open the question of what all these large predators threatening enough for experienced adventures to have trouble and closely packed together will find eat in a dungeon where the bottom of the food pyramid consists of probably nothing apart from scraps of mold, mosses and fungi and generally extremely limited access to fresh water supplies.

Answer 11

Distances are compressed

If you walk around Skyrim or a similar game, you may notice that distances don't quite make sense. There might be a city that takes you a minute to walk across. In other games, there might be a city that just consists of a castle and two vendors. This is usually because of gameplay concerns; walking past a dozen blocks of housing just to get from point A to point B isn't particularly interesting, and there's no need to have a blacksmith that specializes in barrel hoops in the game unless making barrels is a gameplay element.

So, that creates a question: are the cities actually that small, or is the game simply ignoring the boring bits? If it's the second one, then you have a solution; when you fight a group of guards, and see a second group just standing around, that's because they're really a five minute run away. Similarly, the Basilisks on the other side of the cavern are on the other side of the cavern, it's just that the cavern isn't the size of a garage, but the size of an football stadium.

Answer 12

What is exactly the purpose of this question?

Some examples you brought up are so ridiculous that no matter how you justify them, they will still remain unbelievable, as long as we are speaking about real humans or animals. At the same time, in real life, chasing away the danger is far more common than chasing until you kill or get killed, so toned-down version of what you want will have no "video-game weirdness" at all. As I'm understanding it, you want weird and wacky things to happen but also make them believable and those are on the opposite ends of the same scale.

In an understaffed fortress, a melee guard would stare at you from the gate after you kill his friend until you leave his field of vision and then he returns to his patrol, because he doesn't know how many friends you have and what will happen to him, if he doesn't continue to watch his back. Chasing into the darkness after a mysterious stranger who just murdered a trained warrior with no effort and leaving the safety of the fortress walls, would mean certain death. Even when they don't move at all, as you say, it's impossible for a human being to watch a murder and not react in any way. If they, for whatever reason, are not willing to fight you, they will watch you closely and hide as soon as they see you approaching. And if they will still fight you, because leaving their post will lead to fate worse than death, they would still call for help and ready their weapons before you even look at them.

Personally, the least realistic part of that scenario is that guards don't carry a range weapon with them to shoot you while you are busy fighting others, since the point of gates and walls is to stay inside and keep others out, and melee weapons are useless until the opponent breach that defense. Without range weapons, the opponent is not locked out, you are locked in. And with realistic ranged weapons at hand, you better have a very good reason why they are not using them. Since they don't have any more man to spare to chase and capture you, there might be a good possibility that they have no ammunition as well. But again, if you put so much effort into making it realistic, it's no longer "wacky, video-game moment", your guard becomes a real human, frozen with fear, left without means of defending himself and at the mercy of a man who just murdered his friend and is probably coming for him next.

The animals are no different. Just look at a bird defending its nest or an elephant defending its young, hippo defending it's water hole. If they dare to charge and chase off the attacker, they will either land a hit or stop after few seconds and return to that thing they were defending. Even predators that could potentially eat a human won't bother, if they are already well fed. Your basilisk might observe the fight from the distance and hiss because it's defending its side of the room, might try to join but is being bound by a spell or a chain, might not perceive you as a threat, because manticore fights are a regular thing and the basilisk was never bothered by them, since manticore always wins. But in all of those scenarios, it's not strange, video-game logic, it's regular, real life logic.