Depends on the context I think. Step one is for everyone to agree the outcome was poor (or for the client to say so, or the market, or senior leadership, etc.)

Depends on the context I think. Step one is for everyone to agree the outcome was poor (or for the client to say so, or the market, or senior leadership, etc.). Otherwise writing that report is very literally "I told you so", written to make a point. (I do think it is a related scenario where the outcome was fine but you still believe an alternative approach has value; so you then have to make a choice between accepting "my way is not the only way" and moving on or repeating your point)