Without failure, learning is not possible. It's the lessons we learn from them that make us better. One thing that has always helped me is starting small. Set a goal and do not try to take it all on at once, otherwise you will get discouraged and give up. Like if you want to be able to do a 5K do not just go sign up for one. Go for a 5 min walk, then a 10..15.. and so on. Good luck.