Why Do Brownies Crack?

Have you ever pulled a batch of brownies out of the oven for a party and they look great. After they cool you discover a problem. It happened yet again and you wonder, Why do brownies crack? Now what are you going to do? Bring cracked brownies to the party because no one will mind it seems everyone has this problem or do you run to the store and get something from the bakery? It is time to figure this out so we don't run into this problem again. Why do brownies crack? The answer is ...