However, just because a story does not catch the interest of a publisher does not mean the effort is wasted. What I have learned from writing short stories is that they are a very good vehicle for larger, more in-depth projects. I turned that first story into a screenplay and have done so with other shorts. Also, one short story became a script and a novel that is soon to be released as an eBook and POD and a second short story went from a script to a novella, though not yet put into print.
There are constantly ideas running through my head and the short form allows me to put them on paper to see if there is anything to the idea. If a concept for a story cannot be told in 3000 to 7500 words, then it is possibly not such a great story idea.
So, the next time there is an idea rolling around in your head, consider writing it as a short story. It might be the start of something bigger and better. Or it might just fizzle.