I think this answer would really differ from each individual, but here's my thought - anyone that achieves their goals is in, within their own mindset, successful. Growing up, I wanted to have a lot of money and be really strong, today I have achieved both of those things. I'm benching in the 400's, squatting in the mid 500's, deadlifting 600 at 225lbs 9% bodyfat, but yet I'm still not satisfied. Last year I made over $100,000, but I'm still striving to make more money. I'm always trying to find ways to expand or make my home nicer and no matter what I do I still strive for more, constantly adding things onto my truck, but for some reason I'm always wanting to add more. To a lot of people I'm a success, but then I go to work with surgeons that make way more than me. To them, I am not a success, but "average". I guess it all just depends on the individual.