A bunch of small knickknacks (marbles, thimbles, coins, etc) get tossed together in a drawer or pocket, and the hole in the thimble would be like a magnet for a marble that would fit. try to get it out, it jams in further and then you've got a practically useless thimble
Or maybe it was used to contain something, marble being like a bottle stopper. See if there's any weed in it