Bullies succeed by making their victims fear them. The bully may be stronger than the victim, but he does not constantly use force against them. It is the fear of violence or humiliation that makes victims act in the way the bully wants them to. Once it has been established that the bully can hurt the victim, the threat is enough. Maintaining that threat is relatively cheap for the bully and for a sadist this may seem like a good deal. This might also seem cheaper for the victim, because the costs of direct confrontation may be very high.
