There is no one that pushes through only to give up at the end. When you see the end, that is when you put your head down and run it through as what was behind you has been left behind you! What lies ahead is a plain straight road.
One of the keys to success is passion. If you care about something or want it naturally you won't need to force yourself to work on it. The passion will be your fuel. Only work on things you are passionate about.