Reading the article and the comments seems to show that a lot of bullying stems from a distortion of the pecking order.

One case metioned, one person got a promotion that someone else thought should have been theirs; the resentment was taken out on the victim for the loss of esteem or perceived status.

Other cases where the victim stands up to the bully sometimes gains respect and accomodation by the bully; although this may not work if the bullying has gone for a long time. Some aggressive types seem to need a victim to dominate and use as a punching bag and these are the ones to watch out for.