Probably true for most writers, the first rejections were the hardest for me. I questioned whether I was doing what I was meant to do. Having kept at it and edited a few projects as well, I see rejection as a necessary part of the game; there's just not enough space to publish everyone.
Rejection only makes you a better writer if it teaches you to read your work more objectively. Then, from all the feedback you receive and all the times you re-read, you'll be able to do what's best for the particular piece, and send it out again.