well there is so many reason why people bully. its mostly because of their looks, their behaviour and if they are poor. people become bully for getting attention so that they could be more popluar (that's what i think)
to stop someone from bullying. is that the person who is getting bullied must prove them that they are strong and they are not afraid of them. even if they tell thier parents it won't stop bullying. and even if the person is scared of their bully they should be brave and they have to be strong and prove them that their not weak. (make sure you have your friend support you if your ready to face your bully because if you face them alone they may hit you) all the thing for the people to stop bullying is to face their bully and be strong
