Is it possible to overthrow dictatorships?

In the Middle East and in some Asian countries there have been protests against the government, but it is difficult to overcome the military advantage of those in power. It worked in Egypt, because Mubarak was forced out by the military, but this is not the usual case. Without NATO support, the rebellion in Libya would have been easily put down, and even with the support it is proving difficult to unseat Gaddafi. How is it possible for ordinary citizens to overcome both the numbers and equipment that those in power can wield?