Well, that’s depressing, but all artists, all writers, must deal with it at one time or another. Maybe all the time or at least it feels that way. The added problem is that rejection triggers me and other writers I know with old echoes of rejection, humiliation, etc. from childhood. Probably true for most writers because of the reasons we started writing in the first place. I can at least report that as your skin thickens and you maintain the attitude that it is fuel to propel you forward, it hurts and resonates less.
William Goldman famously said about movie making, Nobody knows anything, and I think to a degree that holds true for books. The agents and publishers are bright hard-working people, but no one knows for sure what’s going to sell, let alone catch fire, especially in fiction. Sometimes we have to fan our own flames, twirl our own sticks together on a little pile of kindling in the dark and see what happens. Any one agent or publisher (or review for that matter) is not worth the time or emotion to be devastated. But it still stings.
We are spiritual sharks. We must keep moving forward to live. UPDATE: Leonard Chang has some thoughts on that