How many times have you heard that defensive shootings happen so fast you won't have time to do anything except react?
Usually followed by a dissertation on why night sights, lasers, aimed fire practice are all a waste of time and all you need to be able to do is hit a dirt berm at 3ft. and you're good to go.
Bad guys don't just appear out of thin air.
"He asked me for a cigarette and the next thing I know, he robbed me!"
He was robbing you when he asked for the cigarette. It's just your situational awareness and your ability to manage the initial contact sucked.
The better you are at seeing trouble coming and staying ahead of or at least even with the bad guys escalation the more skill and tactics come into play.
People who think that the only thing they'll be able to do is react... are probably right.