What motivates bullies to pick on people?

Bullies are motivated by the ideas to ruling over innocent! Or because they have such low self-confidence that they need to make themselves feel better by lowering others. There's a story of a bucket of crabs. Two fishermen were watching a bucket of crabs. One told the other that they would never get out. He proved this when one crab was nearly out of the bucket. At that same time, another crab grabbed the leg of the escapee and pulled him back down. Bullies feel so low, that they need to pull down the other people.