Different thing. "I told you so" is a smug, nasty statement. It wins no friends, and closes the ears of those most in need of it.

A postmortem is a clinical, reasoned, and scientific review. Everyone is on board, and agrees to abide by the results.

I worked for a Japanese company, for a long time. I made some colossal mistakes, during my tenure, and was told "That was, indeed, a mistake. We expect you to mitigate it, and not repeat it." Often, I would actually get more trust and responsibility, afterwards.