Not every sentence leads to a story. A gripping, killer opening does not always become a novel. Boy howdy. But I encourage you to stab at it anyway. Craft a line and run with it. Publications are seeking novels, novellas, poems and short stories every day. If you try your hand at short stories--and very short stories in particular--you will see that such a medium has its own challenges. Make a flash.
The terms "flash fiction" and "micro fiction" are fluid, the length of which is established by the publication. In my experience "flash" means than an editor seeks a story between 500 and 2000 words. "Micro" is under that. Actual results may vary and past performance is no reliable indicator of future earnings. So, yeah, it varies.
One online site https://101words.org is a terrific place to try. They are quick to respond and usually offer a few tips about what worked or didn't. When you get a piece accepted you join a group that can offer more feedback. Fire away.