Good writers subbing good work to the appropriate markets still get rejected. Most markets are overrun with subs and have limited publication slots. Subjective judgment and editorial preferences can see good pieces rejected, as can many factors the writer can't control, such as the editor having already bought a similar story.
Perseverence is the key. Story goes out, story comes back, story goes out again the same day.
However, if you're getting nothing but form rejections (no specific comments, no "really enjoyed this, but sorry," no invitations to send more), you might need to recall those stories for revision. SYW could give you an indication of how close your work is to publishable, as could knowledgable betas.