Most fights aren't thought about. Most people trained in any physical activity rely on muscle memory, and the actions are reflex.
Maybe this ability only works on people who are having to give conscious thought to their actions?
Mental Feints, Improvisation
If someone knows about this power (or maybe suspects), they could be mentally thinking about punching you in the face; but they really kick you in the shin.
The insane, drunk, or confused might do mental feints without thinking about it.
Sometimes, this might be improvising. The attacker intended to go for a kick, but at the last second improvised for a gut punch.
Base reaction time for a human is 0.2 seconds. The amount of time for a reaction to take effect (pushing a button, throwing a punch) depends on many factors: how far you're trying to reach, how heavy the load your moving, strength, and so on. However, in many cases that additional time between start and finish of an action is less than the base reaction time.
So, say your opponent has made a subconscious decision to go for a takedown hold. Your hero sees it in his mind, instantly. However, in the 0.2 seconds it will take for the hero to react to the new information, the takedown has already happened.
Many unconditioned opponents (people who aren't doing strength or endurance training) move much more slowly. So, in that case, their may be plenty of time to react to the new information.
Or, maybe the hero also has an improved base reaction time (0.1 seconds).
Mass and Inertia
Based on your stance (standing tall, crouched, fists in front of your face, fists in front of your gut) there is a performance envelope: in 0.2 seconds there is only so far a human being can move those fists to block an incoming strike (for example).
How far is based on body weight and strength. But, for similarly classed opponents, the performance envelopes are roughly well-defined. Fighting classes teach you to recognize these performance envelopes in yourself and an opponent both, and take advantage of them (strike where the defender can't possibly move to block in time).
Even with the ability to see the mind of the attacker, and enough reserve reaction time to do something about it, your hero is still subject to physics. If he (or she) is way out of position (had his fists protecting his face, and the bad guy goes for the gut), there's just not time.