Numbers Are So Fertile Ground for Superstition

It seems that there are a lot of superstitions around lucky and unlucky numbers. Some of those are cultural superstitions, like th number 13, or eight and four in chinese culture. And then there are the personal superstitions people have around their own lucky numbers. Do you have any thoughts on why numbers are such fertile ground for superstition? I mean, there we you can't avoid them. They do come up from time to time.