I know that a lot of folks seethe if I ever mention MBTI. Go ahead keep seething. But all I want to ask is, why are some people predisposed to certain behaviours? That is the behaviours ad defined by P and J in the MBTI system?

Before that faggot barges into the board and speaks of "muh validity" that's not what I'm asking here. I am asking what makes and influences the characteristics of P and J, and why do some people gravitate towards one or the other? Is it a strategy? Epistemology? Drive? Motivation? Or some other thing?