^ exactly

That's what we need to know... there are a lot of signs that you need to look for to know a punch is coming... a punch is quick... if you're only waiting for the glove to move you're gonna have to be amazingly fast to block it...

Spar for ages and all the signs will become part of memory... your opponent moving into range, a look on his face, his left shoulder comes forward so he's gonna throw a right hand etc...

Some people can even defend punches by looking at your feet

Just spar and it'll become instinct... you don't react to the punch but you know it's coming.

Also the defences become instinctive... instead of 'argh he's gonna hit me block it! block it! parry! clip it with your right palm' you just think 'parry'... not even that... you just do it.