Well part of it is local unsupervised hebbian learning, fire-together-wire-together, as it's succinctly put. In particular, neurons will try to fire more like u

Well part of it is local unsupervised hebbian learning, fire-together-wire-together, as it's succinctly put. In particular, neurons will try to fire more like upstream neurons and less like downstream neurons as determined by time-delay in correlation. Then there is also the brains reward center, the one that famously goes wrong when you get addicted to drugs. It releases chemicals which reinforce behavior. And finally some parts are "hard-coded" to be a certain way our DNA.