Okay, stay with me here. It's relevant.
Say I am standing on the road and you are on a train. Okay? Your train is moving 30 mph. You see me go by at 30 mph, right?
You are still on the same train, but now I am on a different train traveling at 30 mph. We are traveling in the same direction. You look out of your window and see me through mine and it looks like we are standing still, right? Same thing happens on the highway. Dig it?
Okay. Finally, we are both on our respective trains. We are now moving in the opposite directions. When I pass you, it looks like I am moving at 60 mph. You can't see me because I whizz by. Right? Same as the highway, again, with cars on the other side. Still with me? Raise your hand if you are not.
Okay. Now here is the relevant bit. You and I are driving (at 30 mph, to stay consistent). You are approaching a stop sign and, because you are too cool for school, you decide not to stop. You are going to blow right through the sucker. Remember our trains? You and I are both moving and we are going in different directions. You look at me and cannot tell how fast I am going, because you are not Einstein and can't figure out the angles and velocities in your head. I probably look like I am going slower than I am. So you, too cool for school dude, blow the stop sign and cut me off. Why? Because you don't understand the theory of relativity.
Get it? Did you follow?
I'm sure you are an excellent driver, but there are people out there (now brace yourselves) that aren't. I'd like to go up in a plane and drop fliers all over the city explaining this theory. Then maybe people will stop at stop signs?