I just did such a stupid thing! It's so stupid, that I have to come here and post about it.

I've collected 21/24 science items. A rare one popped up over by the wood pile. So, I placed a child on it then went to distract the little rascal with another villager. Well, as I was dragging the villager around trying to keep rascal occupied, I accidentally put that villager (a jack of all trades) on the nursery. So, the child carrying the rare science item dropped it and ran to the nursery. Ugh!!!