The motivation aspect of being a head coach has to be one of the more intricate and also incredibly silly aspects of trying to get young people to perform incredible athletic feats on a regular basis. Athletes in general don't seem to have an on/off switch; you have to find the right combination of anger and pride and passion that allows someone to go above and beyond what they might normally do if they're fat and happy and full of burgers.
It's a difficult balance, and because everyone has something different that gets them ready to hit a critical second half three with a minute left or run back a punt for a touchdown or deke five dudes out of their pads to score the game winning goal.