Cliches

How do you know which cliches are true? I always thought cliches were just poetic observations about the human condition, but I'm finding some contradict others. Point in case: "out of sight, out of mind" and "absence makes the heart grow fonder." I don't get it. I know all kinds of people about whom the first adage would apply (I like to call them my ADD friends) but I've always been a victim of the second unless I try to block something out on purpose. Makes me think I'm surrounded by self absorbed people while I spend all sorts of time thinking about everyone but myself. But wait, there's more! Is it just me or does everyone else's head and heart brawl on a regular basis? I can see how they could both be true, but my mind and my heart aren't separate entities. The constant internal struggle between them keeps the people and things that have a piece of my heart in my head all the time. Maybe I'm just a sappy sentimentalist, though....