No one likes to be told that their work is unacceptable, but it is especially difficult to have a creative endeavor rejected. The great majority of people who want to become writers submit one article, poem or short story. When the publication sends them a preprinted rejection slip, the writer feels that his or her worst fears have been confirmed. So, the manuscript goes into a drawer and never again sees the light of day. This is a very big mistake.
Publications reject work for many reasons.
Bad writing is only one of them. They may have covered a similar topic recently, or the publication does not use poetry, or the editor had a bad day and rejected everything that crossed her desk. Or, maybe this particular piece was not up to professional standards. The reason doesn't really matter. It is important, however, to decide at the very beginning of your career that rejection is just one part of the acceptance process.