It's the "verb tense" English supposedly doesn't have, because we call it a "mood."

It's why we write, "If you were a normal person, you'd be boring." (Because, clearly, you're neither of those things.)

You could say, "If I was mean, I'm sorry," but that's like a dead giveaway admission that you were, in fact, mean. And it's a lousy apology. But say, "If I were mean, I'd have left the trap door open, knowing you'd have missed that when you came lunging for my throat after I said, 'Yes, dear, that dress does make you look like a circus elephant.'" (So clearly, you weren't being mean - just pointing out what you'd have done IF you WERE.)

See how that works? Got it now? :D