It's all too easy taking rejection to heart. You get turned down for something and it feels like a personal slight, as if your work or your potential has been denigrated. But you can't rely on the opinion of others to determine your self-worth - that way lays the path to madness. As a writer or any kind of creative individual have to take responsibility for your work, your career and how you feel about what you're doing. Place too much stock in the opinions of others and it'll drive you crazy.
For example, I had a meeting on Tuesday. I won't get into the specifics, but it seemed to go well. Lots of common ground was found, possibilities were floated and I left feeling positive about the future for that particular project. Yesterday I got an email saying I hadn't it to the final round for consideration on something I've been working towards for two years. I abandoned work for the day, knowing exactly what effect the rejection would have.
Getting your teeth kicked in with a rejection is a lot like coping with grief. You get the classic stages: denial, anger, bargaining, depression, acceptance. So I spluttered with disbelief, swore a lot for ten minutes, binned the rest of the day to get over it and felt sorry for myself. This morning that rejection is history. There's I can do about it, better to move on, pursue other opportunities. Sooner you get the grieving process over, the less it'll eat your soul creatively.