The most crushing rejection I ever received ended up teaching me an important lesson about subjectivity, perspective and editor taste.
This was several years ago; I would consider myself still a novice to the business of writing at the time. I had made some short story sales, but only had a few under my belt.
So in the submissions process, I received a very harsh, blunt rejection, particularly focusing on my descriptions and calling them overwrought: "like Paris Hilton's gaudy cellphone." Nowadays, I might have been able to laugh at the turn of phrase. At the time, I was shattered. I thought about trashing the story, or at the very least, trunking it.
Routine saved me here: I have a process for submissions that involves getting them right back into the field, barring certain circumstances, so that's what I did.
The very next rejection letter I received cited a different reason, but praised those same descriptions as beautiful and well-balanced.
I did eventually sell the story: Coldsnap, which appeared in Reflection's Edge - a publication now defunct, but well-regarded during its run.
So I discovered very vividly how much editorial tastes differ, and - perhaps more importantly - that the same story can strike two editors in a completely different way. I'm honestly not sure if I would have noticed this discrepancy if the first letter hadn't been so painful.
But in the long run, I've learned to listen to my gut. I might make changes in response to a review; sometimes, they might be quite the opposite of the reviewer's intention; or perhaps, I might make no changes at all. Somewhere out there, if I am true to the story, there is an editor who will agree ... but I can't please them all.