When I set my glasses down somewhere (say, to rub my eyes) and then forget where I put them. And I can't see them because I'm completely smurfing blind without glasses/contacts.
THAT.
I HATE THAT.
And it's such a Catch-22. You need your glasses to find your glasses...
I had to call my sister to help me find my glasses when I did this once. Humiliating. ;_;