Why do we believe in electrons, but not in fairies?

Why do we believe in electrons, but not in fairies?: "The scientific method is an amazing procedure for incrementally improving certain kinds of theories: those that make testable predictions. A theory that doesn't make testable predictions could still be true, but it doesn't participate in the scientific method. (There are people who believe that the only truths are scientific truths, but this is essentially a religious faith on their part.)"