You can not always wait for the perfect opportunity or wait till you set up a trap, rather you have to just go in. This is courage but it doesn't equate to someone with a killer instinct. Coach had all these little tests to see if someone possessed a killer's instinct. He wouldn't train somebody who didn't have it because he believed the fighter who lacked it would be eaten by the fighter would had it. Here's a real example, today there a fighters who bob and weave under their opponents navel which is an illegal tactic.
Coach taught us to retaliate with a 360 elbow strike to the back of the head followed up by a knee to the head. I'll demonstrate how to set it up in boxing. While the other fighter is rolling head low under your armpit. Drive your right elbow into the back of his neck this is easily done by keeping the right hand in the high guard. Secondly as soon as the fighter touches the canvas knee him in the head. Making sure the rear toe doesn't leave the mat! Then tell the ref the knee resulted from a missed right uppercut.
Most fighters aren't likely to do this since it's dangerous and against the rules. So coach gave little tests, if my fight ended with the other fighter getting cut, he'd make a joke out of it by saying- that cut is a piece of art and if you understood the joke you might have a killer instinct.