Why does it always end in tears?

It's all fun and games until someone comes in the house crying about something a sibling did or did not do.   It's a bit tiring actually.    They know each other so well, that sometimes an off handed comment can send the other into hysterics.     Yep, all 3 of them.     (insert big sigh here)
.    http://assets.amuniversal.com/e03f27802b5e01300649001dd8b71c47