Why do bullys behave like this?

because misery loves company

If you don't validate their low self esteem your not playing 'their' game. I think the minions who follow these kind of people are far more pitiful!

"If you don't bully the person he bully than they'll start attacking you"  What??

BullIES are cowards at heart.

"than" =/= "then"

Standing up to a bully isn't called bullying.   It's called retribution.

@ Veschengo -- That's terrible.  Good for you.   

Bullys are very insecure. They bully others to feel better about themselves. They need to get a reaction to prove to themselves they've caused someone else to feel fear or pain or anxiety. They should be pitied. 

Your post belongs in Social Science-Psychology, NOT Religion & Spirituality. 

probably to make sure people don't start turning against the bully!

what goes around comes around

 Because nobody has the balls to attack bullies in a group.

Here is  a true story .....

When I was 13 I was bullied and beaten up several times; by our school bully

Until the day i took it into my head,  to entwine the school bully in a tennis net and then kick 7 bells of crap out of him...

This i did by simply unfastening one end of the net and running a  complete circle around him by jumping the net myself  Then pulled him over using the net itself and rolled him further in the net on the ground..... Then kicked and beat 7 bells of shite out of him.

I was never bullied at school afterwards. And the school bully tried to befriend me afterwards also.... Though I of course ignored him completely......And went my own way unhindered....

Years later i met the same bully in a bar and he couldnt even look me in the eye..... He became very meek and mild before me instead. And when ignored he sneaked of to a corner table in the bar and sat  and drank alone... then disappeared  to wherever..

All you have to do to beat your bully is something similar.

And the bully will leave you entirely alone guaranteed.... Because he will be scared of you As indeed will also all of the bullies hangers on also, since they fear him....And you have proved he can be beaten.

Its really that simple.

Listen carefully to the following song...... https://www.youtube.com/watch?v=N6RkpLEtSMM