Business and productivity expert Brian Tracy has an incredibly simple, yet powerful practice for knowing when to quit. He calls it "zero-based thinking." I'll let Tracy describe the practice:
In zero-based thinking, you ask this question: "Knowing what I now know, is there anything that I am doing today that I wouldn't start again if I had to do it over?"
If the answer is "Yes," then you should immediately stop doing the activity or try to get out of it as much as possible.
This is something you can practice in your everyday life: is this something I would get into again, knowing what I know now?
That commitment you made to your friend. That recurring meeting that wastes your time. That marketing campaign that isn't contributing to any sales. That business program that no one wants to work in.
It even applies to more personal things: that TV show that isn't cutting it for you. That class that isn't teaching you anything. That book that is so long and boring.
Life is too short to waste it. Become a master at quitting things that waste your time and attention by asking yourself: "Would I even do this again?"