https://www.theguardian.com/careers/2017/mar/28/the-psychology-of-a-workplace-bully
People wrongly assume bullies have low self-esteem, but their behaviour is actually a response to internalised shame. Although some people who live with shame have low self-esteem, those who behave like bullies tend to have high self-esteem and hubristic pride. They attack others to take away their shame – which allows them to remain unaware of their feelings.
Early in life people form different ways of responding to shame. By adulthood, these coping responses become personality traits. Typical coping responses fall into four types: attacking others, attacking oneself, avoidance and withdrawal. When shame threatens people who bully – for example, when they risk looking incompetent at work – they will attack others.
At the extreme side of the scale, people become narcissistic and deal with deeply-embedded shame by attacking others continually.
On the other hand, people who bullies target tend to be sensitive people who are likely to attack themselves in response to shame. Self-blame can maintain a relationship with a bully, but it comes at the expense of keeping oneself a victim.