Decide What You Really Want
It's no good saying 'don't give up' if it's something you don't really want. If you don't really want it then by all means quit, we can't all do everything but decide what it is that you really want in life and then never, ever give up on that thing that you are passionate about.
Failure Teaches You How Not to Do It
Each time you fail at something you really want to do just see it as a lesson in how not to do it. 'OK, so doing it that way didn't work, what other method can I try?' Consider life an experiment. There may be many ways that don't work but if you keep trying you will eventually find the one way that does work. Just keep a note of what hasn't worked and don't keep trying to do things the same way because if you keep on trying to do things in the same way that you failed before then you will not succeed but try to do it a different way and you will learn from your mistakes.
Sometimes it's not so much the process we are following to achieve the results as it is the timing. Some things are not going to happen immediately. Unfortunately we live in an age where we have gotten used to almost instantaneous results and when things don't work out like that we tend to get impatient and give up. The best things in life however will take time so learn to be patient and realize that everything doesn't have to happen overnight.
Be teachable and willing to learn. If there are people who have gone through this process before then ask them how they did it and why they think they eventually got it right. Take notes of the lessons they learned along the way and try to avoid the same mistakes they have already made. As Isaac Newton said, "if I have seen further, it is by standing on the shoulders of giants", learn to stand on the shoulders of those who have gone before and learn the lessons they have learnt so that you can reach further because you won't need to go through the same mistakes. You don't have to do it alone and mentorship is one of the best success principles.
Plenty of people have failed again and again but have gone on to achieve great things with their lives because they didn't give up; they showed patience, persistence and learnt from others. Learn to do the same if you have something you really want to achieve and see failure as your stepping stone to greater things.