As a writer I am always challenging myself to improve. With each new revision, each time I help someone else fill the holes in their story, and each book I read, I grow. My ideas blossom into new stories. The best book I've ever written (to date) was done after challenging myself. I wrote six different books (yes books, as in over 75,000 words each) in a six month period of time. I didn't write these books with the intent of publication. I wrote them with the intent to Challenge myself and grow. In each new book I learned something. I wrote in first person, out of my normal genre, with only one POV, etc.
When the idea for my new book came I'd spent so much time learning that it flowed out the tips of my fingers like liquid. I finished it in 3 weeks and then crited it myself. After that, as many of us do, I sent it off to be critiqued by others, expecting my work to come back bleeding red. The only response I have ever gotten is "This book is Wonderful" with a few minor suggestions.
Many blogs issue challenges, which I frequently join in. Because the more challenges you get into the further you will grow, and the better writer you will be.
EMBRACE the CHALLENGES. Accept defeat. Pick yourself up and go again. I'm cheering for you.