I once received an email from an editor who'd submitted her resume for a job opening at Collegewise, and she did everything but call me an idiot for deciding not to interview her. When she demanded to know my reasons, I pointed out the typos in her resume. She apologized, but when you handle rejection that badly, it's over for the other party.
I've written before about how kids can handle college rejections. But we all face the risk of hearing "No." When a student applies for a summer job, he might hear a "No." When a private counselor is being interviewed by a prospective family, the family might ultimately say, "No" and choose someone else. Independent high schools and colleges hear "No" all the time from students they accepted who ultimately choose to learn someplace else.
When you hear "No," you've got a choice to make. You can voice your disagreement. You can criticize the other party's decision making process. You can get angry, point out every reason why they're making a mistake, and appeal for reconsideration (which almost never works).
Or you could look at it as an opportunity to leave them singing your praises.
You could sincerely thank them for their consideration and for the time they invested in you. You could praise their decision and tell them that while you're disappointed, you can certainly understand why they made the choice they did. You could tell them what you learned during the process and what you're going to do differently as a result of it. And most importantly, you could let them know that you'll still be around if they ever need you in the future.
The second approach leaves a much better chance of you getting invited back for a new opportunity (or if the choice they made falls through). You'll leave a great last impression, one that just might lead to them to recommend you to a friend or colleague who might be a better fit. And you'll actually feel better.
How you handle a "No" says a lot about you. And it improves your chances of getting a "Yes" in the future.