It is important to define perimeters when talking about superstitious beliefs. Some would call religious or spiritual beliefs such. Others would say superstition emplies unwarranted fear.
for the purposes of this tiny blog, lets use the latter as our definition.
I am goddamn unsettled by mirrors. I know, my stupid face doesn't help to boost courage, but it's actually way weirder than that.
I won't look in a mirror unless
A. I fucking have to
B. It is brighter than the sun in the room housing said mirror
C. And not for more than 3 minutes
I know, I know. I'm a goddamn lunatic. But know this before throwing bricks and such.
80% of the population will have full on hallucinations after 20 minutes of staring into a mirror. Sober. I've done it. It sucks my nuts. And lead to "C" mentioned above.
There are conditions known to all like body dysmorphia, which literally cause your optical nerves to misinterpret information on its way to the brain. That's fucked way up. That means in a sense that we see whatever illusion our brain receives from organs developed primarily to avoid being eaten by fucking tigers.
Finally is the light spectrum. The human eye only sees 8%. So 92% of the goddamn universe is invisible presumably because it isn't tiger shaped.
It's an irrational superstition for sure. Lucky for me rationality has never been an important member of my team.