I know its happened to you. Well, unless you never drive a car or you live in a place where there is no traffic at all. You are in a line of cars traveling the same direction and one of the cars way ahead of you, perhaps a half a mile or more ahead suddenly slows or stops and then all the cars behind them suddenly slow way down or stop. All along the line of cars, brake lights flash, tires squeal, and tempers flare up. This exact thing happened to me just the other day as I was sitting in traffic, a car somewhere about 15-20 cars ahead stopped for some unseen reason, and all the cars between us did the same, then me and my rather large truck also came rather suddenly to a stop.
