A root-cause technique that asks 'why?' iteratively until you reach a systemic cause, not a symptomatic one.
The Five Whys is a Toyota-Production-System technique adopted into incident response: when something fails, you ask 'why?' and answer with the most concrete reason, then ask 'why?' of that answer, and repeat about five times. Each iteration moves the answer from symptom toward systemic cause. 'The site went down. Why? Database connections exhausted. Why? Background job leaked them. Why? No timeout on the connection acquire. Why? Library default. Why? Library docs assumed a bounded pool.' That last 'why' is the actionable fix.
Most postmortems stop at the first 'why' and produce shallow action items ('tell engineers to be careful'). Five Whys forces you past symptoms into the system, where the real fix lives. It pairs naturally with blameless postmortems because the structure makes 'be careful' an obviously bad answer.
See the part of the platform that handles five whys in production.