It's normal to find the occasional stray whisker
Cats do shed their whiskers, but only one or two at a time. It's similar to the way that we shed eyelashes. It's normal to find one here and there, but if you start finding a lot of whiskers at the same time, something serious might be going on.
Finding the occasional stray whisker, however, is not cause for concern.
In talking to other cat owners, I have learned that a surprising number of them collect and keep all of these lost whiskers! Some people think of cat whiskers the way they think of baby teeth, as a sentimental treasure. I have to confess, I don't really feel that way. I may pick the whisker up and play with it briefly - whiskers have a fascinating springiness - but then I drop it in the trash.
I have also heard it said that finding a cat's whisker means good luck. Presumably this is because it is such a relatively rare occurrence, much like finding a four-leaf clover. Is it the finding of the whisker that is good luck, or the whisker itself? Sources are divided on the topic. But I did find an Etsy seller who sells cat whiskers as good luck charms. (I hope they are humanely sourced…)
It also seems to me that someone's wand in the Harry Potter novels had a cat's whisker inside it. But I could be wrong about that.
Whiskers are amazing structures. It is difficult for us to understand what it must be like to have whiskers, because we don't have anything similar. A cat's whisker has actual nerve endings inside it, and is attached to tiny muscles so that the cat can "aim" the whiskers in any direction it chooses.
Whiskers are able to physically judge a gap, just like the feelers on a car. But they can also sense air currents, temperature, and barometric pressure drops - allowing the cat to sense, for example, if a moth passes its face in the dark.
Never cut a cat's whiskers! Because they have nerves inside them, this hurts! It would be like cutting off your fingertips or earlobe. If you want good luck, you will have to wait for that whisker to fall out on its own.