This "just do it" mindset is what MA is really about. You've got it first in chi sao, but it's in all sparring - boxing, kb, rolling on the mat, randori, and weapons combat.
It also happens in Street combat - when the training has been deep enough you'll express yourself correctly for the moment at hand and emotions won't get in the way.
When faced with a predator in the wild it's natural to freeze - at night they will see movement first. Unfortunately in a modern situation, freezing gets you killed - that goes for the rabbit caught in the headlights or the man, or woman, on the street facing the aggressive thug. Which is why we put emotional content into the harder sparring sessions. Make it work for you, not against you.
