One of the best pieces of advice I've ever received was: "Never give up!" My favorite Churchill quote is that very encouragement: "Never, never, never, never give up." ~W. Churchill. However, what if giving up really IS the best advice?
Persevering is crucial for success, however, there is no guarantee that you can or will succeed at everything, and sometimes knowing WHEN to quit can be just as important.
Henry Ford said: "If you always do what you've always done; you'll always get what you've always got." If you look around at what you have, is it what you want? Are you making forward progress toward the bigger picture? Maybe it's time to let go of the things in your life that aren't serving you.
Never give up on moving forward, but be courageous enough to move on from what isn't getting you where you want to go.