Our lives are not like the lives of characters in a book. We get born, stuff happens along the way, we die. We only put "The End" when it literally is "The End" - ie you're dead. You may have "failed" at 20, 30, 40, 50...but who's to know what's going to happen when you're 60 or 70?
I know several people who have first got published in their 60s and 70s - are they failures because it happened late to them? Or terrific success stories because they persisted?
I'm struggling to finish my current novel. Deadlines have come and gone and I still can't get the b****r done, which is probably suicidal in the current climate. Is that failure? Will, a couple of years down the line, I be laughing over the champagne as I read my amazing sales figures? Or will I be watching the clock to get to the end of my shift at the check out in Sainsbury's?
Who knows? It's likely to be somewhere in between - a recent programme on chaos theory said that it was impossible to predict what you'd be doing 5 years ahead, even if your life looked ultra stable and solid now. You may be "failing" at the moment, but if an acceptance letter or phone call arrived in the next 5 minutes, you'd consider yourself a success.
Stop focussing on the end, because it won't be the end. Getting an acceptance will lead to more problems to be solved, more failure, more success. It's a bit like being pregnant and only preparing for the delivery. Wake up! You've got the baby around for at least the next 20 years, more if you're unlucky (or house prices continue to rise).
Enjoy the journey, even when it's tough and hard going. Failure and success are only words, they're not states of being and the ending is only the ending when it really is The End. There's plenty of time for living until then.