I'm a success because I set out to write a book and publish it. And I did.
I'm a success because after that book came out, I was begged for more from readers.
I'm a success because people have messaged me to tell me how much they liked my books & some have said how my book impacted their life.
I may not have made a best seller's list, or be making enough money so my husband stops calling my writing a hobby, but (as the above part said) my books have affected people. My books have changed the way people think about themselves and their relationships, or about other people (speaking about my MM books here and that I've been told by some readers that they never really saw gay men as having the same kind of love that straight couples do, but they do now! *joy!*)
Sure, my writing could use stronger editing and maybe more digging in, but I'm learning. My degree isn't in English or Creative Writing. I have a degree in Psychology. I think I've done pretty good so far. (or is it "well"? I've done pretty well so far. *shrug*)
I am a success.
Furthermore, even my most beloved authors receive really harsh reviews. I just remind myself that not every book is for every person. Diversity is the spice of life. And that which doesn't kill you makes you stronger.