I always told myself that I wasn't a short story writer, that I didn't want to write short stories, and that I couldn't enjoy them....until I started doing it.
Admittedly my first few short stories weren't really "stories" because they didn't have any kind of arc with them. I think a good rule of thumb for novel writers that helped me is that when you start writing short stories, start out with only 1 or 2 characters, one problem, and one scene. Obviously as you get better at keeping yourself in control you can expand the amount of scenes and plot threads. But it's a great way to practice.
I cannot even begin to articulate how much of a difference and an improvement I've seen in my longform fiction since I started writing short fiction this year. I write tighter, I'm better at trimming, and even my descriptions are better. I tend to get to character a lot quicker.
And honestly, above all, writing and submitting short stories has been a fantastic excercise in teaching me how to deal with rejection. The first few hurt SO BAD. Now I'm up to 42 rejections since March, and when I get one my brain is like "meh, next one..." and it makes it feel SO MUCH BETTER when you get an acceptance--or hell, even an editor that rejects you but says nice things! I had a rejection from Flash Fiction Online that I couldn't even really be sad about because the editor in chief sent me two flipping pages of notes on my story, what she thought I could improve, etc.
And as with novel writing, the best way to get good at writing short stories is to read the heck out of them. One of my favorite magazines current is Daily Science Fiction. If you join their email list, you get a story in your inbox every day (it's free!). It's a SFWA qualifying pro-market, so the stories are pretty solid, and they're all under 1,500 words. Think of it as a daily lesson for your brain on how to do a lot with a little.
JJ is right. Take a smaller idea. Stick to one scene and roll with that.
Try it, try it, try it! At the end of the day it is writing practice, and your writing muscle needs different kinds of exercise
(can y'all tell I'm a total convert or what)