People are bullshitting just the same about topics they know nothing about. They often also won't shut about when others tell them and even when they themselves know that they know nothing. To some extent this is necessary for humans to function at all, and the scientific process starts out from uneducated guesses and rigorously refines them and casts away what doesn't hold up to empiric data.

Optical illusions are evidence of the pile of hacks that our senses and our consciousness use to make sense of the world. I think it is really difficult to fully disengage from the biases this induces, and we are sadly best at perceiving such flaws in others. This might be one of the reasons why humans have to socialize with other humans to maintain mental health.