Everyone gets rejected at some point. Don't take it personally because it isn't meant personally. Rejection is about the employer's needs and whether you fit them; it's not about you or your qualifications. And it doesn't mean that you will never work for this employer; in the future, their needs and your qualifications will change.
It's possible to turn a rejection into an informational interview. You may wish to consider contacting an employer that sent a rejection letter and politely asking whether they are willing to talk with you about what else they would have liked to have seen in your resume or in your materials. If you choose this route, make sure you thank the person for the feedback and reiterate your interest by saying something like, "If your firm's needs change in the future, I hope you'll reconsider me."