In a story I've been thinking about, the actual power of magic in the world is literally limitless. There is only a single person who actually figures this out, and it terrifies him so much that he uses this limitless power to remove magic from the world. However, I can't really figure out a plausible reason for why he in particular was able to figure it out, and why no one else was.
What plausible reasons could exist for limitless power not being seen as such?
I remember reading an article 5 or 6 years ago about Tony Hawk, a pro skateboarder. I don't skateboard, so I don't remember the specifics, the overall gist of the article was pretty interesting.
The author outlined several records which Tony had set. He'd been the first to perform a fair number of skateboard tricks - he'd set the bar at the world level. However, after he proved that certain tricks could be performed, many other non-pro level skateboarders were able to replicate his success.
The author essentially concluded that Tony was not necessarily the best skateboarder in the world, but that he had the vision to try and perform tricks and moves which others simply didn't. They would copy him after he "invented" them, but did not innovate themselves.
And thus, you have your answer. If magic is largely a self taught discipline which is sufficiently difficult to learn, then it's quite likely that most practitioners simply never envisioned magical applications on a large enough scale, or did, but didn't personally have the ability to pull that vision off.
Similarly, sometimes a "simple" goal can be achieved in a very convoluted way. It can become ingrained in a society that said process is done in that way, and no other, until an outsider points out that there's actually a very easy way to achieve that result if you only tackle the situation differently.
And so, your hero might be the only person to realize that in order to cast a spell you need not necessarily tap into your own personal energy, but the energy, of say, the Sun, and thus have the ability to do anything you wish.
He was raised outside the dogma that created the "rules of order" for magic. Perhaps he's a wild talent instead of a school-taught mage. Or perhaps he's just that one rebel who refused to honor the taboos associated with magic from eons past, when the first mages realized "Oh, crap, this stuff is dangerous. We better tread carefully in how we pass this knowledge down..."
So in that sense, he's not the first. Just the first in so long that no one else has records of it.
OR those records exist but are deeply hidden. But somehow he found those records where the first wizards built a framework to protect the future generations?
If you assume that finding this limitless power is possible but not terribly easy, you have a reason why this was not discovered by accident in the remote past by people unknown.
There will always be a first. If the first person who discovered this power immediately chose to remove it from the world, then that means nobody else will stumble upon it. If once removed that power cannot be restored even by the same person who removed it, then that's it: no magic for anyone, ever.
I think it all depends on how magic actually works, what its basis is, etc., as well as what you want to go with this plot. It might be that all this first person did was disguise magic or make it very difficult (not impossible) to find again.
There are many possible reasons why something is not discovered until a certain point in history. For example, the source of magic in your world could come from a "magic portal" that happens to be in an uninhabited continent or island, or it could require that the magician ingests the flowers of a certain plant that only grows on a given spot. As well as it's not obvious, it could work.
One plausible reason could be that he in particular is able to manage the insane amounts of magic required to sense how much magic there is in the universe - maybe an organelle (a sort of midichlorian) to detect magic. Maybe due to a virus, he gets all of these midichlorians. This would also allow you to make him be constantly sick - he has a virus that cannot be beaten, and while this gives him lots of magical power, it makes him infectious and feeble.
The second reason could be that one must stand at an exact place to sense all of the magic. This could be achieved by having the magical power somehow stored far away, but all on one horizontal plane, so one must stand at an exact point at an exact time to sense all of it (and not have it blocked by the Sun).
It very much depends on the time period. If it's middle ages, then you could say that people were afraid of anything that messed with the status quo, and so the majority of mages just stuck with what they knew. This can extend to modern day, but you'll need a taboo or laws to keep people from trying.
You could also say that the flow of magic wasn't "wide" enough for us to see thru it to figure it out.
Every human has an energy gate through which energy flows freely in and out. There's a limit to how much energy can flow, so making powerful spells takes longer and it is tiring/boring to store energy for a while, so people generally never went up from 1min except in rare cases.
This man discovered that dead people's energy gates explode in size letting huge amounts of energy flow through. He then performed several experiments on live and dead people in his pursuit for the truth. In the end he constructed a spell which would expand the gate without actually killing you.
With his energy gate expanded he could flow unthinkable amounts of energy through him and cast huge spells in seconds. This led him to believe that someone might figure this out in the future so he used his newfound power to shut down everyone's energy gates.
People had always tried to reanimate the dead, but no one ever succeeded, so people started thinking some sort of deity would take the souls away as to not let reanimation exist. This man was different though, he wanted to understand why it actually didn't work.
After studying the dead for a long time he theorized that the gate would just shut off, however after some testing it was clear that this was not the case and instead the gate would expand.
