I have been using a "house" analogy as well.

I give my Public key to Fred to feed my cat while on vacation but I don't trust Fred. It doesn't matter because when he unlocks my door he can only see what I've "done" - the stuff I have inside my house. But it's all frozen in place. He can't even move a chair much less steal anything.

I open my door with my private key and everything is unfrozen and I can more furniture at will etc. because I unlocked my door with the private key.