Vanishing stamps

I once bought an enormous bag of stamps at my local thrift store. Hundreds of mostly worthless stamps, but I thought they were cool. So I was sitting on the floor, at home, sorting them out. The more pristine/kindamaybe valuable ones were going into glassine (wax paper) envelopes, sorted by country or region.

So as I'm sorting, I put one of the envelopes down beside my knee. A few moments later, I find a stamp that I want to put inside. When I reached, without looking, to get the envelope, it wasn't there. Maybe I adjusted and it wound up under my leg when I moved? Nope, not there. I stood up. No envelope. I counted the other envelopes I still had. Nope. None of them had the stamps from the one I wanted, either.

After looking for a few minutes longer, I gave up. There wasn't anywhere else for the envelope to be. It simply wasn't there anymore. I never did find the envelope I lost, not even elsewhere in the house.