I would suggest that this 10% (or lower I suspect) portion be the ones to look to for judgement then. Self critique is not reliable in my opinion. Even if one is a harsh critic of oneself, one may not have the requisite knowledge to know if one is doing well or not.
One can develop the requisite knowledge. Part of that process is seeking feedback from the right "10%", something a lot of photographers fail to do. Fellow forum posters seldom fall into that 10% category IMO. I've seen too many threads full of "nice shot" responses to someone posting a rather mediocre photo.
The biggest obstacle to overcome in developing realistic self-critic is emotional investment in the image. I have a
lot of photos of my kids. I regularly go back through them and assess them with the same expectations I use on photos for clients. I find that in retrospect, I rated some photos higher than they warranted because they are of
my kids and so they were great photos from a personal point of view, but not so much objectively.
When I cull through the shots from a concert, I am in fact looking for those "WOW factor" shots because that is what the client and the public who view the photos expect. Of course, not all of the photos I select have that factor: some are selected simply because they are a photo of a back up player or offer an angle that an audience member wouldn't normally have a chance to view. Still, I can tell at the time of capture when I have a potential "great shot", and that is usually reinforced when I'm looking at the image on my monitor.
Your mileage my vary and kids, don't try this at home. The ability to self critique adequately to please clients takes a lot of failure based experience and time spent looking at what are good and great photos, and especially learning
why they are great.
Therein lies the truth of your statement about not having the requisite knowledge: many people haven't learned why a given photo is great, at least from the standpoint of being able to give a sensible, point by point critique. They go no further than "I really like it". That's an alright attitude, because not everyone who picks up a camera needs to develop the critiquing skills of a curator for MOMA or Hamilton's.