I think that people bully because they have low or weak self-esteem; they feel bullying is an opportunity to detract from their own perceived shortcomings; or because it makes them feel superior, accepted or included with the "norm" or mainstream by singling out individuals who are considered very unique or different.
Oftentimes, bullies are, themselves, the victims of abuse; and instead of efforting to rise above their circumstances by vowing to conduct themselves with honor and integrity, they succumb and surrender to their plight by becoming abusers themselves. They are, in essence, mimicking how they've been made to feel (or conditioned to believe is true of themselves) by perpetrating bad acts against others perceived as weaker or more vulnerable than they.
This enables the bully to feel powerful, in control, and even omnipotent...until they are compelled to face the reality of their predicament or are held accountable for their actions.
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