We are always using observations to refine our mental representation of the world. We are confident about some of our theories and less confident about others. As we encounter evidence for and against those theories, our confidence in them adjusts accordingly. How much you believe something after you see the evidence depends not just on what the evidence shows, but on how much you believed it to begin with.
We might like to think that our beliefs are based on evidence alone, not on some prior preconceptions but in reality nobody forms their beliefs this way. If an experiment provided statistically significant evidence that a new tweak of an existing drug slowed the growth of lung cancer, you would probably be quite confident that the new drug was effective. But if you got the same results by taking cancer patients on a day-trip to Stonehenge, would you accept that the ancient formations focus vibrational earth energy on the body and stun the tumours? No, because you are not insane. You have different prior beliefs about the two theories and as a result you interpret the evidence differently, despite it being numerically the same.
This outlook explains why getting five reds in a row on a roulette wheel (RRRRR) feels less random than RBRRB even though both are equally improbable. When we see RRRRR, it strengthens the theory that the wheel is rigged to land on red. When we choose our theories, we like simpler ones better than more complicated ones. We do not have a nice theory for RBRRB so we ignore it. This is not irrational, without some biases we would run the risk of walking around in a constant state of amazement. Nobody wants to feel like they are tripping on LSD their whole life.
Conspiracy theories work by eliminating the validity of information that debunks the theory in the first place. Suppose you watch a viral video on Facebook which proclaims that COVID-19 is caused by 5G. At first, you may be slightly convinced but then you encounter more information: countries without 5G have cases of COVID-19; it is not possible for electromagnetic radiation to spread a biological virus and many more. Each of these pieces of information reduce your confidence in the conspiracy theory until you dismiss it entirely. But conspiracy theorists are not as stupid as you may think, in fact, they are very good at manipulating people.
One major tactic of conspiracy theorists is to combine their theories with the ultimate conspiracy theory – the government, the media, scientists, universities and corporations are all in on the conspiracy theory together. The combined conspiracy theory package will be harder to believe at first, but it is unphased by new information unlike in the previous scenario. This results in cult-like followers willing to go beyond liking and sharing Facebook posts.
On December 4, 2016, Edgar Maddison Welch, a 28-year-old man arrived at a pizzeria and fired three shots from an AR-15-style rifle that struck the restaurant’s walls, a desk, and a door. Welch later told police that he had planned to “self-investigate” a conspiracy theory. The conspiracy theory in question claimed that the pizzeria Welch targeted was operating a human trafficking operation including the sexual abuse of children linked to the Democratic Party. Welch saw himself as the potential hero of the story, a rescuer of children. Instead he was arrested and proven embarrassingly wrong. In an interview with The New York Times, Welch later said that he regretted how he had handled the situation but did not dismiss the conspiracy theory, and rejected the description of it as “fake news”.  Even when all of the evidence was against Welch, he still defended the conspiracy theory.
Never hold on to any beliefs too strongly and be cautious of any information you see on social media. Don’t be a Welch.