Because of cognitive dissonance. In psychology, cognitive dissonance is the psychological stress experienced by a person who has two or more contradictory beliefs, ideas, or values. In this state, specific neurons and neurotransmitters trigger a defensive state when feeling that our thoughts have to be protected from the influence of others.
No matter how valuable an idea is, the brain has trouble processing it when it is in such a state.
On a neural level, it reacts as if we’re being threatened, even if this threat comes from harmless opinions or facts that we may otherwise find helpful and could rationally agree with. But when we express ourselves and our views are appreciated, these defensive chemicals decrease in the brain and dopamine neurotransmission activates the reward neurons making us feel empowered and increasing our self-esteem.
Our beliefs have a profound impact on our body chemistry, this is why placebos can be so effective.
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