OK mine...
I have a large to do lead pile and collection of boxes in the basement of projects 'to do'. Some of them have come from bring and buy or eBay as well. So when I know I got a package for the current project BUT you just can't find it, that is very annoying...
Maybe it's a sign of having too much stuff - but that's a statement the Mrs would say not a true hobbyist. However, I have searched and searched. It's so annoying to know you have a good set of toys which need paint, you are in the mood to paint them, but you can't find the Frecking things...
ARRRGGGG...
Pretend you are not looking for them. That might help. Then go through the box you are positive they are not in. Usually works for me.
The reverse is when you find something in the lead mountain that you had forgotten you had ever bought and then enjoy painting and basing.
Currently have 'lost' a complete mid-C19th Austrian army. Can you feel the empathy?