Maybe it was the environment, that a lot of these people could be better if supported the right way? Or to say it simply (and please understand I know nothing about you so it is not meant as a criticism of how you personally work), maybe it was because they worked with you?

I would also say that throwing x% and hiring again does not work well. The pool you are hiring from is people that are not happy somewhere else. You are not getting a 90% chance of finding a "good" person.

I would venture that you really can't if you want to be accurate and fair.

You were on the ground, which to me implies that you had a local view of the rate. In your area the observed rate of mishires apparently was around 10-20%. If you were in another team/part of the org you might have thought 50% or 0%.

My guess is that HR does exactly this sort of thing. Someone did a study once and averaged numbers that were obtained 'somehow' and that is then simply applied.

Like stack ranking. Everything is a normal distribution, right?

If you ask me: What large orgs are not good at is doing what actually makes sense. It's too much work and there is so much that could go wrong anyway. The way out are blanket policies implemented by drones, bean counters, the odd psychopath etc.

I observed the local rate, correct. I didn't really make a claim that a large org would be exactly the same as my local rate, so I agree with you that it could differ. But honestly, I do believe it would be over 0.1 for most orgs, just based on my experience with people in college and other areas of life. Competence at a high level is really rare and most people just are really not good at complicated tasks, even many graduates from top schools.

I definitely would agree that a lot of people in large orgs are unfortunately like that. I can corroborate that from having been in many of those. I can also attest to the fact that most managers don't deal with this. There is a lot of moving people around or simply ignoring the problem.

Now like my earlier sibling mentions, just because someone isn't a top performer at their current job at the current time doesn't mean they can't be great in another area or can learn. I have (and had) a bunch of people on my teams that were/are not senior people but they have a smart brain on their shoulders, are inquisitive and learn. Sure they don't know our stack fully, they don't have the exact same opinion on how to write code etc. but they are able to learn and adjust and maybe teach us where our customs aren't the best as well. And we teach them too.

I'm speaking of practices like at large banks where people have been hiding doing nothing but being on Facebook all day for 10 years and all that has happened is that every project manager tries to avoid getting these people assigned to their projects.