I work for a FANG level company and when a person is promoted to a higher position and it doesn't work out they'll get let go or moved back to another position,

I work for a FANG level company and when a person is promoted to a higher position and it doesn't work out they'll get let go or moved back to another position, I've seen it happen multiple times and it's happened to me personally. This isn't their decision, higher ups demand performance. This "principle" seems to ignore this completely: that employees are regularly evaluated for performance. I don't see that addressed at all in the telling of this story. Yearly performance reviews and KPIs are a thing for most professionals. When people underperform and performance is the norm the rest of the machine will correct. I'm sure in more dysfunctional or institutionalized orgs are going to work differently, but it only takes a few empirical examples for me to just completely discount this as something to expect. I believe the research that proves this is likely flawed as well.