[AaronBrown]

There are two worst cases to check.

First is if you have an absolutely marginal calling hand. With n players in the pot, your chance of winning is less than 1/n, but close enough that the amount already in the pot makes your call attractive. In this case, by raising you lose the different between 1/n and your chance of winning. That can't be very big preflop in hold'em, but in later stages it can be crucial.

The other bad situation in when you will drive people out of the pot who will pay you if you hit. This also can't be very big preflop in hold'em since even the worst drawing hand can become powerful on the flop, and even the best made had can be undone by a flop.

You can't lose much by raising when you should call preflop in hold'em, while you can lose a lot by calling when you should raise or fold. You can play good poker and never call, but you can't play good poker and always call.