I let them play for a while alone, depending on the size of the bet to my stack. I am talking from a tournament point of view. You are not the only player at the table at some point someone will call or raise with a premium hand and with any luck you will see their cards. No one can have great cards time after time, however, and you don't want to get caught and lose your entire stack. Protecting your blind is often a good place to start your calling or aggressive stance, although they may be out by then.