How does someone gain or maintain power?

Have you noticed how some people seem to have power over other people? Well I have. I've been trying to think if why people let others have power over them. The main reason I can think of is because they are afraid of them. I mean, I know if I'm afraid of someone, i let them walk all over me because I don't want any problems. If you are really that afraid of someone, it is really easy for them to have control over you. They maintain power by instilling fear into you and so you don't have the mind set to tell them off. People that have power shouldn't abuse it. The people trust them enough to have power and when they abuse it, it;s so wrong. I don't understand how people can be so heartless.