There is a class of things that people understand takes practice, which includes things like skateboarding, playing the violin, speaking a foreign language, and so on.
There is another class of things that people think don't require practice. They think that the first few times they try them, they will get a good idea of whether or not they have a talent for it. This class includes drawing and writing fiction. They are wrong.
To expect that your first short story is going to be good is like expecting your first time playing the violin is going to sound decent, or your first few times on a skateboard halfpipe are going to work.
The truth is that writing, drawing, improv, and a whole lot of things requires practice. Nobody is born a good writer. You need to write or draw a lot to get any good.
The depressing thing about it is that you need to put in the hours, making bad stuff, just like you need to practice playing the violin. It's not that talent is not a factor, but a big part of what makes someone a good artist is not their natural talent for the art--it's their determination to keep practicing even when it's hard to do it.