It's not the perception of "randomness" that is a problem, it's the arbitrary figure attributed to getting fired with no comment on methodology or the attributes that will get you fired.
We assume there would probably be PIP for those individuals in this hypothetical scenario. However even then, saying "10 percent of our workforce will guaranteed be subject to PIP and or firing as a matter of our staffing methodology" instantly turns much of your working time into fluffing your work and backstabbing colleagues.
OR running away at great speed.
OR telling investorts "We do not grow, we abritrarilly trim regardless of market forces."
AKA, GE.
