Quote Originally Posted by Sutekh View Post
Stormtroopers seem to operate by Law of Conservation of Ninjutsu rules, in that the more of them there are, the worse they are, as the amount of accuracy and competence is divided amongst all the Stormtroopers present.

Maybe the electromagnetic fields generated by their blasters energy bolts repel each other, so that when a half dozen troopers are aiming at the same target their blasts are subtly pushing each other away and making each other miss. (Meanwhile, Imperial QA testing is firing them one at a time, when they are perfectly accurate, and passing the blame on to the Stormtroopers, since they are engineers, and Imperial engineers always blame the user for product deficits.)
I know this was tongue in cheek, but there actually is a potentially viable in universe explanation for why otherwise competent, and possibly even effective Stormtroopers suddenly and spectacularly fail when they are pitted against the characters we tend to follow in Star Wars. The Force itself. Remember, while it doesn't appear to have any kind of consciousness as we understand it, the Force does have a will, and a way of bending events towards outcomes. The Force is most definitely not with most stormtroopers (Finn excluded, obviously). So, we could take it quite literally, that the Force is subtly influencing stormtrooper aim and effectiveness in order to ensure that these agents of the Dark Side are unable to hit targets who matter.

It's an odd thing to think about, but George Lucas basically baked plot armor into the nature of his universe.