People believe what they want to believe. Show them facts that disprove one of those beliefs, and they will believe in it even harder. The problem is that most people are not scientists. People who do science are trained to believe in something because of observation, but then to try and disprove it. Few non-scientists understand this. Experiments are designed to disprove their favorite hypothesis. This makes them especially open to accepting new data and discarding a "belief".
People spend many years in graduate education to become PhDs so they can learn this. Unfortunately, sometimes they don't and will cling to a favorite hypothesis long after it has been disproved. These folks try to design experiments to prove their hypothesis, which is NOT the Scientific Method. I have observed this, especially in medical research, and a physician near retirement age trying to prove something he started to believe 30 years before is sad.