Some times you have to bluff, but there is the added advantage that if you play the same way when you are not bluffing then you can get callers and some times the really dumb player who is a bigger bluffer than yourself and decides to go all-in.
You don't need to go all-in to make a bluff either because if you make your bet on the River just the right size, they will think you are trying to get that little bit more out of them, Too big and you chase the fish away, too small, and they will call your bluff, so it is a fine balance between making a bluff and making it look like a bluff when you are holding the nuts!