Balloons

Hearts are also like those cheap balloons you used to get from carnivals. For a while you'll play with them and toss them around and what not. And then when you least expect it, they'll pop. And you'll cry because you were so sure this balloon was going to be your best friend. You'll naively try and put the pieces back together but you'll fail.

You're never going to want a carnival balloon again because you're afraid of the popping noise it makes when it explodes. That's why you have to be careful with carnival balloons and likewise with hearts. Because once that balloon is gone, you're never getting it back, and that.