It's always discouraging when a door closes, and doors close all the time.  It can be difficult to stay positive in the face of people who don't like your work.  It takes time and determination to refine your work to a level of acceptance or else to find an appreciative audience.  What sustains us, though, should be the pleasure of the journey.  If we truly like what we are doing, then the process is its own reward, not just (or perhaps despite) its outcome.

Oh, no, here I am having to be mature again! :)