I think it's because someone suggested that some of his fish choices were not compatible.
It sucks when you see a fish that you would like to have and then realize it's not compatible with your reef/other fish/inverts or what not. The worst is when your tank is too small to house the fish. Then you just feel like going out and getting a 180 gallon tank and spending your life savings. Maybe that's just me. But it sucks.