Also, run for one's life. Depart as fast as possible, either to escape danger or to reach something quickly. For example, You'd better run for it before the teacher catches you, or The bully is coming after you--run for your life! The for it in the first term almost certainly means "for one's life"--that is, to save one's life, a usage that can be literal or hyperbolic. Also see for dear life; make a break for it.