You will not succeed at bluffing each and every time. Cautious opponents will notice when you are caught bluffing. When other players discover that you do not have a legitimate hand in every bet, your good hands will most likely face more calls than they would if you left your opponents with the false impression that you have never bluffed at all.
That is in fact one of the advantages of bluffing. Not only will you be able to get a pot from time to time, but even if you fail to bluff once or twice it can be used as potent advertising. Consequently, a player who bluffs every now and then should expect to get more money on his good hands as well.