The employee made a mistake and you just paid for them to learn about it. Why would you fire someone you just educated?
Nobody gets fired: learning opportunity for next time, but little direct incentive to improve.
Fire someone: accountability theater (who is really responsible), loss of knowledge.
AFAIK, blameless postmortems and a focus on mechanisms to prevent repeats seems like the best we’ve come up with?
The employee made a mistake and you just paid for them to learn about it. Why would you fire someone you just educated?