Usually bullying occurs when one is differen from society as in unique whether it is your interests, talents, looks, or even religious background in a certain communities they asses people to a certain degree and if people don't fit that they are labeled an outsider which causes bullying. Although this isn't always the case it is one of the most common causes of bullying.
Another common cause of bullying is envy or jealousy for instance if you have certain talent, something you are good at and someone else perhaps sees this and they have been working towards that talent/goal and you just have that talent this could lead to them being jealpous or envious of you. So instead of accepting that you have achieved this goal and working on themselves because they feel threatened by you they may start rumours about you to bring you down so they feel better which can lead to one getting bullied.
I know it's rather long & I'm not quite sure if this response actually answered your question. I hope this helps :)))
