Each person responds differently to a story or poem. It could be that you've named your hero Fergus and the editor reading your story was tormented at school for years by someone named Fergus. Most editors are intelligent people, however, and should be able to rise above this sort of thing. The thing to keep in mind is that there are factors beyond your control that you can't hope to anticipate that will prevent a particular story or poem from being accepted by a particular journal. These considerations aside, you can control the quality of the work you send out.
Some journals return comments with the rejected manuscripts.
This can be helpful, though, admittedly, not always. The thing that one reader objects to in your work might be the very thing that another reader finds most appealing. This can be difficult if you've just finished a piece. However, when you receive your story or poems back from a journal, even if there are no comments attached, read over the work with a clear, detached eye. After the passage of many months you might spot something immediately that you were unable to see when you submitted it.