Humans don't have instincts, except a little baby's instinct to suckle. An instinct is a pre-programmed behavior, not a desire. Only non-human animals have instincts.
Motivation is never something to overcome. Motivation is power. You work with it.
By "willpower" people usually mean ability to force yourself to do something you aren't motivated to do - you shouldn't try to do that, it's operator error of the human system.