Back in the recesses of my mind is a faded memory on training that I received in the U.S. Army. The good sergeant told us that there are three types of knowledge: those things that are necessary to know, good to know, and nice to know.
He related it to throwing a hand grenade. It’s absolutely necessary that you know how to pull the pin and throw it. It is good, but not necessary, to know that you have four seconds from the time the spoon flies off until it explodes and that the grenade has a fifteen-meter burst range and a five-meter kill radius. And after everything is said and done, it’s nice to know that what you’ve just thrown is a M-26 fragmentation grenade.