One piece of advice for aspiring writers which I have repeated in the past is that if a slush pile reader, or editor, gives you ANY feedback in a rejection, it's worthwhile. They will not take time to comment unless the story "grabbed" them to some degree.
Another point is that, if you are a good writer and have some small degree of objectivity, you will recognize when the comment is valid. Over the years there have been many times when a story comes back to me with a comment that strikes a chord.
If something bothers you or makes you uncertain in a story, and the rejection mentions the same point or problem, it's a confirmation.
Of course, some people run their stories through critique groups and have these glitches highlighted BEFORE their stories are submitted. I've lived in small rural towns all the time I've written fiction, so that option isn't available to me.
Today I got a rejection from a pro publication which illustrates my point. It said, in part:
"Your characters and the premise... are strong. However, the tale could be made more urgent if it were lived/shown for the reader a bit more, rather than relayed through dialogue."
Ah-hah! This is great feedback. You see, I write dialogue well, and now I realize that in playing to my strength as a writer I stinted my reader as a storyteller. With this insight, I can go back to the story and do a little rewriting and probably make it a lot better.