The fear of the number 13 is common enough to have its own phobia named after it. That isn't to say, however, that everyone walking down the street fears the number. This phobia, known as triskaidekaphobia, dates back centuries and is loosely related to the fear of Friday the 13th. At points in history, the fear was so common that groups of people began to develop clubs dedicated to debunking it; they would meet on the 13th day of the month at the 13th hour just to prove that nothing bad would happen.
Triskaidekaphobia has many roots, many of them historically accurate and others simply mythological or altogether false. A common myth is that the 13th article of the Code of Hammurabi was omitted, but in reality, the code was not numbered. Others believe the fear has biblical origins; the 12 apostles gathered with Jesus at the last supper, and Judas was the 13th person to sit down at the table. Judas later betrayed Jesus. But even in Christianity, the number 13 is not necessarily bad or unlucky, and in fact, the Bible has references to the number 13 in a distinctly positive way.
The fear of the number 13 may actually stem from more severe conditions like anxiety, depression, or other negative emotions that are simply irrationally focused on the number. Superstitious people may have difficulty keeping calm on Friday the 13th, for example, because they fear it is an unlucky day that is destined to doom them or others. Many Italians believe Friday is an unlucky day to begin with, so combining the day with the number 13 creates the feeling of bad luck.
The best way to overcome a phobia is to see a professional who can help the sufferer target the real cause of the fear. Anxiety medications exist that may be able to treat the problem, and a professional may be able to come up with a series of steps to help the sufferer cope with his or her issues. Anxiety and depression can become serious problems, regardless of whether the sufferer has a fear of the number 13 or some other focus for his or her difficulties, so a professional should be consulted in these cases.