People believe what they want to believe

• Everyone has a model in their head of how they think the world works. That model is built mostly from what you've experienced and what people you trust have told you. But everyone has different experiences and a different set of people, leading to different models.
• We also believe something if our income or approval in a social circle depends on believing it.

It is then essential to understand that no one thinks independently. We all suffer from some degree of blindness.