No because those two have a idea behind it.

Walking under a ladder is dangerous, since that area is where you are most likley to drop something. So people that walk under ladders have a higher chance of getting something dropped on them then those that walk infront of it.

Mirrors were expensive as fuck back in the days. Breaking one as a working class person would take several years worth of hard work to repay. Thus, several years bad luck if you break a mirror.

Black cats are cute as hell. But there have been stories around that people could only turn into black cats, that black cats were men that were turned when they were wooed into the forest by the spirits, naughty children that did not as they were told and so on. Black cats have had a bad reputation in some cultures, others not so much.

Ireland (I think) see them as good luck, that steems from celtic mythology. Japan see also them as lucky. USA, being a melting pot of a lot of Europeans and what not, took that with them as they went over. The bad luck story overtook and here we are today.

So there you have it.

Edit: I am sure someone will call me out on something in there and say "NU HUH! THIS IS HOW IT IS!" and I want to say right now that I will never love you less for it!