Elementary reasoningTo escape predators primitive man made decisions quickly. Once habits were established they were followed w/o question. It's safer to mistakenly identify a predator than to mistakenly ignore a predator.
Social adaptation to primitive societies involved acquiring beliefs from peers, especially leaders. There was no need to question beliefs provided they seemed adequate. Rationalizing was generally adequate to support beliefs. Skepticism was okay as long as it didn't disrupt group dynamics. On the other hand, disruptive skepticism might be severely punished.