Nor do people hold questionable beliefs because they are stupid or gullible. They are the products, not of irrationality, but of flawed rationality. Streaks of successive hits or misses may stand out and be remembered, while sequences of frequent alternation between the two may go unnoticed and be forgotten.
People have faulty intuitions about what chance sequences look like.
People expect sequences of coin flips, for example, to alternate between heads and tails more than they actually do. Because chance produces less alternation than our intuition leads us to expect, truly random sequences look too ordered or 'lumpy'. Things that go together should look like they go together. Spicy food is the cause of heartburn, not the bland food we had. Sometimes this is not a bad principle, but the overapplication of it is when it gets us into trouble.