As my favourite statesman Winston Churchill said "Success is not final, failure is not fatal: it is the courage to continue that counts." He also sagely said "Success consists of going from failure to failure without loss of enthusiasm." I personally suspect the optimist can find success more easily than the pessimist. (There's a Ph.D. in that topic I bet)
But what a heck is success? I can't define yours - you can't define mine. I can't even tell you for sure how Brody defines success tho I am pretty sure there are a whole lot of cookies in his mental image of it. My definition changes. Yours probably should too. This year agility success might involve getting all my equipment set up and playing agility at home. In 2008 it involved winning a national title. Range is good. Variation is the spice of life.
Another, tangentially related point I have addressed before is that success with one dog may not be success with another dog. Having Sam do a short successive series of jumps and tunnels is success for us. Running clean and fast and happy over a masters level course is success for us. Success for Dora is keeping it somewhat together for a day. Success for her brother Gade is a title/
As I processed this topic a warped line from a song kept running through my head. "Success what is it good for? Absolutely NOTHING". Not quite true perhaps - but it certainly doesn't have to be the driving force (at least in the traditional, how everyone around you defines it sense of the word). Define your success. Develop a plan to achieve it. Use "failures" as stepping stones to it. Be prepared to redefine it and rewrite the plan as needed. Enjoy YOUR success!