Accomplishment will make you feel good about yourself. To overcome quitting, trick yourself. A 3-hour marathon may be nearly impossible to run, but 10 runs of 18 minutes each is more reasonable. Break things into small, achievable goals. When the 5 minutes are up, you can bargain for another 5.
Frustration is much easier to bear in small doses.
This will help convince your body to hang in there until the job is complete. Even though there is no guarantee of success in any other area, there is a guarantee of spiritual success. And that knowledge helps build confidence. And no matter what the outcome, each successful step undoubtedly improves your self-confidence and keeps you on the road to success. You start to feel restless and uncomfortable.