Whether it is unlucky or not, people will always fear it or dread it, and some embrace it. No proven thing here; but one description I observed was that when you move the 3 to the top of the 1 and then rotate it so that it is not vertical but horizontal, then it appears to look like the devil's pitchfork. Just looking like that in a time when science wasn't prevalent, struck fear into people, and superstition is born.
The idea that the number 13 is considered unlucky is a superstition. There are many different kinds of superstitions, based on things in nature, charms, spirits, objects, colours, accidents and so on.
But there is probably no superstition that has as many people observing it, in one way or another all over the world as the one that number 13 is unlucky. Many hotels don't have a 13th floor; the count goes from 12 to 14. Some hotel rooms do not have a 13. Many people would never have 13 persons at a dinner table.
Yet the strange thing is that there is no single, accepted explanation for the origin of the superstition about 13. There are many different ideas about the origin of it. Some experts say 13 was unpopular from the time when man learned to count. By using his ten fingers and two feet as units, he came up with the number 12. Beyond that the 13 was unknown and frightening to him. Among religious circles, the 13 superstition is traced back to the Last Supper, at which were Christ and the twelve Disciples, 13 in all. Another strange thing about 13 is that this number is regarded as lucky by the ancient Chinese and Egyptians.
There are many instances to prove that number as unlucky and so you can't simply ignore it as a superstition. Even in races also that plays very prominent role. So F1A banned the number 13 to the race cars after the disastrous death of a person who has that deadly number on his car. It was so significant that a phobia namely "trescodecophobia" is named after it.
