The Reason for Trolling

Hello fellow bloggers. Lately I've been thinking about the people behind trolling and there's one thing that I'm still confused on: what's the reason? I feel like the many levels of trolling all have different reaosns behind them but I'm talking about the big massive major trolling. What exactly is the reason or mortise behind this type of trolling? Do people do it to seek revenge on someone they feel has wronged them? Do they do it simply because they like seeing the pain of others? Is it because it's their instinct to have that insidious tendency to be mean? Or is it because they are insecure about themselves and are taking their insecurities out on others anonymously? It could also quite possibly be a combination of all these reasons. I want to know your opinions my fellow bloggers. What do you believe the reason behind the big harmful trolling is?