Why do people cause problems for themselves and others?

War and Conflict are human created words. Some people cause problems for others because it gives them a sense of power, most of the time I have no idea why people introduce brand new problems into the world because not only does it not benefit them in any way, it can come back to haunt them in the future. Like when there is peace, there come certain people who start problems and everything gets messed up. Like for example computer viruses. One person creates a computer virus and other people start to do the same thing. Soon it's a computer epidemic and they themselves wish they had never done it. Why do some people just have to create problems/obstacles for themselves?