According to a Harris Poll conducted for the National Organization on Disability in the USA, about two-thirds of people surveyed believe that "split personality" is part of schizophrenia. But medically speaking, "split personality" has nothing to do with "schizophrenia".
In fact, there are many myths about schizophrenia.
First, that schizophrenia is caused by bad parenting, and lack of moral fibre. The straight answer is that we still don't fully understand the causes of schizophrenia. We do know that there is a genetic component, and that there are some poorly-understood environmental and biological triggers.
The second myth is that people with schizophrenia are unstable and violent, and could go "wild" without any warning. The vast majority of schizophrenics are not a threat to others, just like the vast majority of non-schizophrenics.
Third, that you can never recover from schizophrenia. To the contrary, many cases are treatable. Indeed, hope in a recovery is part of the treatment.
A fourth myth is that schizophrenics are mentally retarded. Nope, schizophrenia and mental retardation are entirely different conditions. Schizophrenia certainly can cause problems with abstract thinking and concentration, but it does not lower your intelligence.
Fifth, that schizophrenia is caused by witchcraft, or evil spirits, or demonic possession. Nope. Neither is schizophrenia God's punishment for the sins of a family, nor is it a result of unrequited love.