It Depends
I archive all my stuff but most photos are not seen by anyone...
I'll save nearly everything I shoot because I'm a pack rat - - but most of it will never be seen by anyone but me.
Generally speaking, I find that my yield varies inversely to its cost. With digital, I'm willing to experiment more, so I'll easily blow a half dozen shots on something trivial, or perhaps 50 shots on a promising wildlife opportunity. I would have never done this with film...especially back when I dabbled in medium format.
Since I still shoot 35mm film for underwater, and that that environment is generally challenging (exposure settings), I'd say that my expected yield is usually around 1-4 shots per roll of 36...5-10%, but sometimes it is this low because of environmental conditions, but sometimes just because the day didn't have anything particularly or profoundly new/different that made for a significant and noteworthy composition...as such, I could have technically correct exposures with nice compositions, but it was "just another ho-hum day", so I'll relegate these as inferior to my first ever roll of UW film, because that first roll carries special memories whereas this one didn't.
And it has been said that the difference between the Amateur and the Pro is the size of their trash can. Probably a better question to ask is: "what percentage of your stuff do you feel is good enough to show to others?", for this is really a question that's a combination of both your technical skills as well as how tough you are on yourself.
Overall, I would say that when I'm not experimenting, over 95% of my stuff is technically proper for exposure, focus, etc. Probably 75% of this has reasonably acceptable composition, so we might say that my yield is around 70%.
However, I'll always cherry-pick through them and cut at least 50% out and usually more: good isn't good enough: I'm looking for excellent or better, particularly when it comes to subjects I've already tried a few times.
For my Tanzania trip, from roughly 4,400 images down to somewhere around 600 (15%?), and I was finding that I was increasingly brutal as I went through them. I then culled through these keepers (IIRC) twice more to get it down to around 200 in total, which would be a final yield of around 5%.
Overall, I would say that if you're cutting down to around 10%, you've been a tough reviewer of your own stuff...and probably have cut 3x-5x more than most casual shooters today.
-hh