I got a rejection email the other day, and I have to admit they don't hit as hard as they used to. Part of it may be that I've received enough rejection letters by now that I've come to view them as nothing personal - which is how a writer SHOULD view them. The story submitted to an open call has to compete with dozens, maybe hundreds of other stories. It may be one of the best stories you've ever written, but it may not be as good as the top 25 stories vying for 20 slots in an anthology. Also, the story may go in a direction that the editor doesn't care for. No reflection on the quality, just not what the editor is looking for.
That doesn't make it a particularly positive experience for the writer unless one thing happens: if the editor makes any comments about the story at all, you as a writer know you've got a good story in the making - it just needs a little more polishing. Editors - like everyone else - don't have enough disposable hours lying around to offer helpful suggestions to the hundreds of people who send them stories in the hopes of becoming a rich and famous author overnight. When one does take the time to comment on the story, it's a sign of something very good.
Me? I've only had one such comment from an editor, and I'm still trying to sell that particular story. The comment was that it was a story they liked, but a little too long for their needs and didn't quite mesh with the direction of the anthology. They invited me to feel free to submit stories to them again. To a struggling writer, that kind of encouragement is like gold!