My wife came to my workplace to drop off some papers I needed and she had to sign in and sign out of the office. When she was leaving, I verbally said the words “don’t forget to sign out” and my brain threw some kind of exception (I don’t know what kind since I don’t use undocumented APIs). To me, signing in and out has always been something done on a computer. I had never realized before that signing in/out had a real world analogue and it blew my mind.