I am about as ambivalent as as a metronome when it comes to rejection letters. I've gotten a few on various work. One did stimulate my mind concerning a picture book story for children. Publishing house said, "this story is really cute, but we cannot use it at this time." It was a seasonal book, but not really. One rejection letter wanted to introduce me to an agent. I wrote, he wasn't interested.
The other side of the metronome is self publishing. I've tried that as well. I was not pleased with the product and pulled the book from production after about fifty copies were sold. Amazingly, used copies of my first publishing effort are still selling on the internet for between 30 and 50 dollars. I guess you could call that a cult following to a minor degree. No matter which way you try to move your manuscript to the general public, there will have to be personal effort, (book signings ect.) made to make a name for yourself. There are two main reasons folks want their books to be a hit. Fame and money. If you don't care about fame, then that leaves the obvious other, and that's enough to keep you in there plugging away.
--edited by Rob Emery on 4/2/2014, 12:55 PM--
In my proposal for a short story collection I let the first publisher know that I was a personal acquaintance of one of his star authors, which was nearly true, and I knew that the author was too polite to dispute it if called. Maybe that had something to do with the encouraging tone of the rejection. He said something like, "I can't see a way to make any money on these stories, but somehow they have to be in print." He was telling me not to change the stories, just to find someone with a different business model. A valuable lesson.
The second publisher has a different business model, and was happy to take the book, and the second book too.