Today I was going to write a bit about reaction time and it looks like ol' Journeyman and i were thinking the same thing. So read his post here first.
I was actually thinking about this because Journeyman and I discuss this point a lot, and I consider him my teacher in many ways. He's a modest chap, but he has experienced much in his field of work, and I value his opinion on "real life" situations as much as anyone I've ever met. And although we break techniques down, discuss options and what not, Journeyman has always said one thing regardless of a person's level in martial arts: Do Something! Do anything! Just make sure you react.
A good example is from a punch. The attack comes, the uke blocks the strike, then fails to control the attacker. Of course control is very important, but at least you stopped the attack. You are not hurt, and have bought some time to default into plan B. Or you are asked by an instructor to do hip throw from a hook punch and you freeze up and execute body drop--it still worked, and you didn't end up a deer in the headlights. And hurt.
So, for this reason, we always execute some form of technique from an attack, even if it's not even close to what we were asked to perform. Then we laugh, the uke reloads, and we try it the way it is supposed to go.