Failure is just your current Personal Record (PR). It's your goal line. The next time you attempt that same activity, you know what you have to do to improve your PR. Without failing one time, it's impossible to know if your goal is reasonable. It could be too easy, or too hard. Try to look at what you DID do, rather than what you did NOT do.
I know this is easier said than done. This is my philosophy of fitness, but I have to keep reminding myself to do it. I have to constantly remind myself of what I can and have done, to squash the thoughts of what I didn't do. Even though I have to do that every day, it's worth it in the end to know that I have accomplished some really impressive things, and that's just the foundation for doing even more in the future.