How Well Do You Know Your Keys?

Something I thought of today:

I find it weird how we familiarize ourselves with our keys. I don't have a special key cover to differentiate between all the keys (I have four) on my keychain, but I can tell you which one opens up what. For me, I just KNOW the difference between which key I'm looking for if I need to get the mail, unlock my apartment or use at my parents' house.

So then I thought about how if I were to give someone my keys (if they needed to use my apartment or something,) they'd have to like, hold on to the specific key I say opens my apartment, because otherwise they'd have to go through all of them - afterall, they don't KNOW my keys like I KNOW my keys.