Why is it?

Why is it that some people think that traffic/road signs don't apply to them? Signs with messages like, "Stop," "Yield," "No left turn," "No right turn on red," are all there for a reason. In my many drives through Georgetown I am convinced that certain people have absolutely no conception of what, "Stop, All (Four) Way," means. When the sign says, "Yield to underpass traffic," that means that you must yield to the cars coming out from the underpass, not cut them off. Do these people have a death wish? Or maybe they are out to hurt other people? Who knows. I certainly don't understand it.