The Hidden Process of Human Behavior

I wonder to what degree someone's output is not determined solely by their explicit value function, but something some hidden process that goes on in the mind. It's a shame we sort of have to treat the mind as a black box just since we don't have reliable brain-computed interfaces and stuff like that. You're right, there probably is some internal stuff that you just lose and you can't explain the totality of human behaviour just by looking in from the outside. I guess that was behaviourism's big downfall, right? But yeah, I guess.