Our psychology is flawed, "Be yourself" or "Follow your heart" are probably some of worst advice one can follow, because "yourself" or the personality traits you were born with are not idea by default.

Our psychology fools us, drives us to seek comfort, pleasure, and guarantees, ending up miserable (look at the majority of people).

Our bodies improve and evolve by confronting our natural drives and emotions, waking up early and hitting the gym is guaranteed to boost your happiness almost immediately, compare this to going out on a long night drinking where you end up miserable the whole next day.