Yeah. Like I said, I'm very interested in that stuff XD

Also, I looked up the broken mirror one. Here's what I found for it.

"The origin of the "break a mirror, face seven years of bad luck" superstition can be traced back to the Romans, who were the first to create glass mirrors. Just because your culture invents something totally useful like a mirror doesn't mean you can't still have some irrational beliefs about its use. The Romans, along with the Greek, Chinese, African and Indian cultures, believed that a mirror had the power to confiscate part of the user's soul. If the user's reflected image became distorted in any way, this could mean a corruption of his or her soul."

And the superstition about black cats varies from place to place and per time period. Some of this I knew already, and some I just looked up. Ancient Egyptians worshipped cats in general, but especially black ones. In Scotland a black cat’s appearance at a home signifies prosperity. Pirates believed if a black cat walks towards you, it’s a sign of bad luck, but it’s good luck if it walks away from you. And in the English Midlands, a black cat as a wedding present is thought to bring good luck to the bride. And the big one about a black cat crossing your path started with the Salem Witch Trials when people began believing that witches could turn into black cats.

As for luck, it's random, but some people are naturally luckier than others.