People are extremely ready to generate beliefs about the world

Beliefs are an essential part of human cognition. People by default have a strong desire for cognitive closure (a made-up mind). Keeping an open mind is difficult, but

Just comprehending something is often enough to believe it, and therefore to have it affect our behavior. Therefore your Default beliefs about any topic are likely unexamined but still affect behavior.

References:

• Toward Parsimony in Bias Research: A Proposed Common Framework of Belief-Consistent Information Processing for a Set of Biases

From the paper:

Children understand (and thus believe) something takes place long before they have developed the cognitive capabilities that are needed to deny propositions