It's pretty common to have one or two episodes of psychosis and then not again. Selection bias and all that. Anyone that doesn't have a severe chronic problem, you're not going to be aware of, but it's reasonable to assume there are more mild cases than severe cases of almost any condition. For that matter, it's a definitional issue - people can appear crazy temporarily for almost infinite reasons, and if it doesn't reoccur, even doctors aren't going to call it schizophrenia. You go into a hospital appearing to be stark raving mad, they are going to test you for drugs and call it "schizophreniform" if they can't find any.