Lock and Key
I don't understand my door's locking mechanism. I have discovered that I can lock myself in my room in such a way that I can't get out without somebody letting me out.

This reminds me of a fun riddle. Imagine two people (Beth and Stephanie) in a country with an extremely corrupt government (Molly). The corruption has spread as far as, and beyond, the postal service. In order to send anything through the mail safely is to send a locked box. Without being able to communicate with each other, how can Beth safely send an arbitrary item to Stephanie without Molly intercepting it?
So for example, say Beth sends a package to Stephanie. Then Molly can just swipe it. If Beth sends the package in a locked box, she must also send the key, without it being intercepted, bringing us back to the same problem.