I was rejected by Knox Burger not once, but twice. [Full disclosure: only the passage of time allows me to think about this without getting depressed.] When I was trying to get an agent, he rejected me. And then by the time I had an agent and had written Learning to Fly, he had some kind of relationship with my agency (he would have been about 70 then) and before they started sending it out to editors, they asked him what he thought of it. Not much. [Full disclosure: again, the only thing that makes this bearable is that that the book went on to starred reviews, sold through multiple printings, got optioned for film - never made, but we don't have to mention that part, do we? - and was named one of the best books of the year by Library Journal.]
Here's the rest of the article on Knox Burger.