The easy "no's" have been the grammar challenged entries, with openings that aren't effective or with sentences that are hard to understand.
The others, I say no to, usually lack "story" -- the sense that there is a start, an end, and progression for the narrator from one point to the next.
It's a rather non-gratifying experience--I never know if I am failing to provide value or not. But it is a learning experience since I am seeing a larger collection of writing than I am used to. And aha, my subscription to River Teeth arrived not long ago, and I had the chance to read through today, not just the better examples of essays, but those narrowed down to the few that actually made print. Was their luck involved for the authors? Did they have a special flair with words? Did a gnarly voice grab my attention? Were they on someone's bump to the top list? Just what was involved in these final pieces that made them leap ahead?
The first thing I noticed in pretty much all of the stories I read, was complexity of thought, feeling, situation within the story. These were not flash fiction, a tale hinting of something changed but fully fleshed. Most of the stories ran several pages and the authors needed all of the pages to tell the tale. There was no, just this one moment with this sweet kiss, type of tales. The narrator worked to make sense of connected events. These were all tales with mature writing.
One never doubted the narrator. This was the narrator's tale from beginning to end.
Some used artistic styling--subtitles, or time stamping, to pull the story together, but these were not necessarily required although they added to content rather than subtracted.
Many used snatches of memory from their entire experience, grabbing those that made the most connections.
Most used situations that I had never encountered in my life:
-- the student at a remote campus working on their degree-- "In Other Words" by C. Levison McGuire
-- the writer visiting a person dying who didn't have family or other connections, "Susan Cox is No Longer Here" by Justin Heckert
-- the daughter whose mother took photos of her then left in a divorce, "Evidence" by Jennifer Lunden
-- the active woman suddenly incapacitated, Jan Shoemaker
This is perhaps why creative nonfiction offers value to others--it allows them a peek into the humanity of other lives.
Some things I reject in my own writing are those that want to capture me entirely as a human person; instead I rely on the situational experience in all its complexity. Simplifying down to one strand in a web of day to day life is not easy to do. It means creative nonfiction is all about selecting events that are important and knowing how they connect through choice to a shift in view--the essence of storytelling.