In Guangdong Province, where I live, the number four is very unlucky. Luck is much more meaningful in this land of chronic Mahjong addiction and bus cooties. Compassionate belief in luck rather than personal responsibility is the leading cause of suicidal motorcycle riders. People here avoid the number four like they avoid public trash can use. The reason is linguistic.
Guangdongwa (Cantonese language) is the prevalent language here even though Potonwa (Mandarin) is the official Chinese language. It is a completely different language from Mandarin and has more tones than a Nokia cell phone. It is apparently impossible for almost anyone to learn beyond childhood. I know Chinese people from outside the region who have lived here 20 years who have never been able to learn the language. The language lacks many consonants so common in English, which gives me great job security. They have no "sh","r", "v", "th", and their words do not end in the letter "l". I may seem to digress, but the reason four is bad luck is because of tones and an unfortunate choice of a syllable.
The number four and the word "death" are the same except for a slight difference in intonation that in virtually indecipherable to the foreign ear. One, two, three, DEAD, five, six, etc. This goes for other numbers with four in it like "deadteen","deadty","dead hundred and deadty dead", etc. People will avoid living in an apartment with a four in the number, and will almost never purchase one. They are convinced, just as sure as you will get bus cooties from a warm bus seat, that premature death will occur if you live there. (We live in #404 and are still alive two years later.) By all means, you want to avoid hospital room or bed that has a four in it.
You wonder what they were thinking when this language was evolving. When they got around to forming the concept of numbers, why in the world would they come up with dead to mean number four? Did they run out of sounds by the time they got to numbers? Maybe they just needed a number to mean something bad since they are so superstitious.
In English we have our own number quirks. One (I won!), two (I just went #2), three, four, five, SEX!