a) to avoid facing up to their inadequacy and doing something about it;
b) to avoid accepting responsibility for their behaviour and the effect it has on others, and, 
c) to reduce their fear of being seen for what they are, namely a weak, inadequate and often incompetent individuals, and,
d) to divert attention away from their inadequacy - in an insecure or badly-managed workplace, this is how inadequate, incompetent and aggressive employees keep their jobs.

Bullying is an inefficient way of working, resulting in disenchantment, demoralisation, demotivation, disaffection, and alienation.

Bullying...
is a form of abuse, and bullies often go to great lengths to keep their targets quiet, using threats of disciplinary action, dismissal, and gagging clauses. What bullies fear most is exposure of their inadequacy and being called publicly to account for their behavior and its consequences. This makes sense when you remember that the purpose of bullying is to hide inadequacy, and people who bully to hide their inadequacy are often incompetent.

A bully is a person who

• has never learnt to accept responsibility for their behaviour
• wants to enjoy the benefits of living in the adult world, but who is unable and unwilling to accept the responsibilities that are a prerequisite for being part of the adult world.
• abdicates and denies responsibility for their behaviour and its consequences (abdication and denial are common features of bullying)
• is unable and unwilling to recognise the effect of their behaviour on others
• does not want to know of any other way of behaving
• is unwilling to recognise that there could be better ways of behaving.

Bullying is obsessive and compulsive; the serial bully has to have someone to bully and appears to be unable to survive without a current target.

Bullies are seething with resentment, bitterness, hatred and anger, and often have wide-ranging prejudices as a vehicle for dumping their anger onto others. Bullies are driven by jealousy and envy. Rejection  is another powerful motivator of bullying.

How do bullies select their targets?

The bully selects their target using the following criteria:

• bullies are predatory and opportunistic - you just happen to be in the wrong place at the wrong time; this is always the main reason - investigation will reveal a string of predecessors, and you will have a string of successors
• being good at your job, often excelling
• being popular with people more than anything else, the bully fears exposure of his/her inadequacy and incompetence; your presence, popularity and competence unknowingly and unwittingly fuel that fear
• being the expert and the person to whom others come for advice, either personal or professional (ie you get more attention than the bully)
• having a well-defined set of values which you are unwilling to compromise
• having a strong sense of integrity (bullies despise integrity, for they have none, and seem compelled to destroy anyone who has integrity)
• having at least one vulnerability that can be exploited
• being too old or too expensive (usually both)
• refusing to join an established clique
• showing independence of thought or deed
• refusing to become a corporate clone and drone

Jealousy and envy are strong motivators of bullying.

Personal qualities that bullies find irresistible

Targets of bullying usually have these qualities:

• popularity (this stimulates jealousy in the less-than-popular bully)
• competence (this stimulates envy in the less-than-competent bully)
• intelligence and intellect
• honesty and integrity (which bullies despise)
• you're trustworthy, trusting, conscientious, loyal and dependable
• a well-developed integrity which you're unwilling to compromise
• you're always willing to go that extra mile and expect others to do the same
• successful, tenacious, determined, courageous, having fortitude
• a sense of humour, including displays of quick-wittedness
• imaginative, creative, innovative
• idealistic, optimistic, always working for improvement and betterment of self, family, the employer, and the world
• ability to master new skills
• ability to think long term and to see the bigger picture
• sensitivity (this is a constellation of values to be cherished including empathy, concern for others, respect, tolerance etc)
• slow to anger
• helpful, always willing to share knowledge and experience
• giving and selfless
• difficulty saying no
• diligent, industrious
• tolerant
• strong sense of honour
• irrepressible, wanting to tackle and correct injustice wherever you see it
• an inability to value oneself whilst attributing greater importance and validity to other people's opinions of oneself (eg through tests, exams, appraisals, manager's feedback, etc)
• low propensity to violence (ie you prefer to resolve conflict through dialogue rather than through violence or legal action)
• a strong forgiving streak (which the bully exploits and manipulates to dissuade you from taking grievance and legal action)
• a desire to always think well of others
• being incorruptible, having high moral standards which you are unwilling to compromise
• being unwilling to lower standards
• a strong well-defined set of values which you are unwilling to compromise or abandon
• high expectations of those in authority and a dislike of incompetent people in positions of power who abuse power
• a tendency to self-deprecation, indecisiveness, deference and approval seeking
• low assertiveness
• a need to feel valued
• quick to apologise when accused, even if not guilty (this is a useful technique for defusing an aggressive customer or potential road rage incident)
• perfectionism
• higher-than-average levels of dependency, naivety and guilt
• a strong sense of fair play and a desire to always be reasonable
• high coping skills under stress, especially when the injury to health becomes apparent
• a tendency to internalise anger rather than express it

http://www.bullyonline.org/workbully/bully.htm