When you need to tie your hair, change, wash your face etc and you have to take of your glasses, one of these could happen...

1) Walks of to do something else and completely forgets to put glasses on.
2) Walk off and realise that you are partially blind, return to the last place you saw your glasses, and they're gone.
3) Do what I did recently and accidentally drop your glasses, shuffle back trying to look for them, and accidentally step on them.....

Mine were Rayban tho.... :C

Good thing I have a backup. :/