You are traveling down the highway, when you come up behind a big truck.|
You're in no particular hurry, so you decide to stay behind him.
If you get close enough you won't have to watch for traffic, just tail lights.
Pull up about one car length from his bumper.
Don't get back too far, as someone may get in front of you.
Now just sit back and relax.
You've got nothing to watch for, nothing to do but cruise.