I put my glasses in my shirt pocket last night.
I wore them driving home, then left them on my desk.
In the morning, I woke up, and put them on sometime in the morning.
I am going throughout my day, whistling to myself...
I see a speck on my glasses, and decide that I am going to wipe down the lens really well, so I can just poke at it with my finger. I am doing this absentmindedly as I am typing on the computer. So I remove the smudge on the lens. I think to myself, "hmm, lemme rub the other lens too", so I stick my finger on the other lens.
I poke myself in my eye.
The lens had fallen out in my shirt pocket and I did not notice it all day.
(I have one "bad" eye, and one "good" one)
It turns out the missing lens was for the "bad" one. I had assumed since I did not notice it was becuase it was for the good one, but as I wrote this post I checked, and it was the bad one.