"You think you're tired? You don't even know what tired IS. Try having FOUR kids. When you have FOUR kids, you'll wish for the days with two kids! Two kids is a piece of cake!"
I think we can all agree that would kind of stink, right? First, it completely invalidates A's feelings and brings the attention to B. Second, A might never have four kids! Which means that their exhaustion or frustration will never seem paramount, or even legitimate, to B. A's feelings and experiences don't count. Ouch, right?