When you're making a turn or changing lanes, you signal. This way, other drivers on the road won't have to wonder why you're slowing down, or drifting into their lane. It's simple courtesy to let other drivers know when you're going to make this kind of move, which makes it baffling to me as to why so many drivers don't bother. If you're one of these people, please realize that signaling your turns and lane changes does not make you less of a man/woman, and does not require much effort. Use your turn signals and help make the roads just a bit safer.