Postmortems are necessary for learning and should be held whenever an incident occurs 1. You can determine if you need every incident in some short description or skip it for low-severity ones. You must always be sure that nobody is pointing fingers and the whole process is blameless.

Best Practice: Avoid Blame and Keep It Constructive 2 Blameless postmortems can be challenging to write, because the postmortem format clearly identifies the actions that led to the incident. Removing blame from a postmortem gives people the confidence to escalate issues without fear. It is also important not to stigmatize frequent production of postmortems by a person or team. An atmosphere of blame risks creating a culture in which incidents and issues are swept under the rug, leading to greater risk for the organization

Another important thing is data 3. Your investigation has to focus on hypotheses and analyze data using scientific method. Finding the Root Cause is always challenging.

We can continue how to set up the postmortem process 4, and inspire there from the best.