Yesterday's question: If something catches you off guard, it means that you didn't expect it. You were surprised/you didn't see it coming. Examples from the web: He's got a lot of tricky moves, so make sure he doesn't catch you off guard! The soldiers moved in quickly,hoping to catch the enemy troops off guard. I think I caught him off guard when I told him I was resigning.
Learning is hard work, but everything you learn is yours.