How Do Writer's Measure Success?

Do you think being published is success?  What about getting a fan letter?  Is success measured by the numbers?  How many books you've sold?  How big your advance is?  What about your skill level?  Have you taken a look at things you wrote in the past? 

Have you edited the work you've done in the past?  Yeah, we all catch things we don't see when we leave it for a while, but have you considered that you learned more than before and that's how you can edit that old piece?  Take a look at something you did 2 years ago, or even 6 months ago and look at it.  Any mistakes you see now might not just be because you were looking at it so much before, but because you didn't have the knowledge to look for it.  Or maybe your impressed with how well you did! 

Perhaps old stories have something to remind you or something to re-learn.  But measureing sucess of an unpublished author can be tough.  How can one measure the expansion of the mind?  Perhaps only by the words we chose. 

I'd like to think my success is the reaction of readers.  My success is having two friends argue at the dinner table about the two main characters in a heated debate forgetting that I'm the one that wrote the book.  When they both look at me and ask who's right, I'd say--both of you.  Because writing is about expressing thought meant for you to think.  When a writer has readers thinking that, for me, is true success.