It was a really insightful article about post-mortems, but not in the context of software engineering! It was written about post-mortems in hospitals (where the term originated from!) and it had several useful insights that were applicable to software engineering, too.
The one insight I do remember is that it said something along the lines of: "In a sufficiently mature enterprise, all failure modes are complex because all of the easy failure modes have preventative measures in place".