Never quit. My book, Chicken Soup for the Soul, was turned down by 33 publishers. It's since sold millions of copies.
I used to define success as being able to produce any result you wanted, whether it was a relationship, weight-loss, being a millionaire, impacting the culture, changing society, whatever it might be, it might be homelessness, whatever, but lately I've realized that success is "fulfilling your soul's purpose."
My definition of success is "the fulfillment of your soul's purpose."