As much as I dislike the forced attrition mechanism, people putting in 110% are not going to be forced out. It's the people putting in 30% that are going to be the attrition targets.
My 30% could be somebody else's 110%, though that's not the likely scenario we're talking about.
What if instead, some people put in 110% by putting in 14 hour days and others are judged more harshly who have family or other obligations. This is how we get an industry of 20-somethings with no lives other than work. In a forced attrition scenario, if I were on a team with people significantly younger than myself, I would be shitting bricks.
I was noticeably older than most of the people in my team in Amazon, and I was never shitting bricks[1]. The ones not reaching performance targets were always crystal clear to _everyone_. If you can't spot the underachievers, maybe that's the time to worry.
Despite how detailed the Amazon interview process is, people slip through the gaps and you end up with someone who somehow can barely write functional code, let alone maintainable code. Or you find the person is capable of writing code, just maybe not today, or tomorrow. Is the day after good with you? There are much more interesting things to be doing on-line instead of writing code.
[1] I was reminiscing with a co-worker in the kitchen one lunchtime about the respective things we'd had to do to deal with the Y2K bug at the places we'd been working at. Another talented and very capable developer co-worker overheard us and commented "I'd never even touched a computer before, back then."
The industry is not expecting mechanical engineers to actually do advanced work fresh of university but somehow in some places programmers are thought of as a ready worker package for the sewing machines.
I'm also yet to meet these programmers who can't code. There are plenty of engineers that barely can code though, but they don't call themselves programmers. And there are plenty of inexperienced programmers that can't code and if they won't learn they will drop out for other positions.
There's a difference between "can write code" and "will write code" which is what I was more intending to express in my post.
Everyone that gets a Dev job in Amazon has to be able to pass multiple loops where development skills will be tested.
To put it another way. You should be focussed on maintaining and motivating the top 10%, not on getting rid if your bottom 10%.