Where are you getting "hardly" from? In this example, it normally would have been P0 (release-blocker) but was downgraded to P1 (still the second-highest priori

Where are you getting "hardly" from? In this example, it normally would have been P0 (release-blocker) but was downgraded to P1 (still the second-highest priority) because of a special consideration on the customer's end. The point of severity is that it's an objective metric determined in isolation based on specific technical guidelines that any developer on the team can follow (such as https://www.chromium.org/developers/severity-guidelines https://www.chromium.org/developers/severity-guidelines). Whereas priority is a higher-level determination that isn't purely technical. It's like the difference between body fat percentage and attractiveness. Any "engineer" (doctor with a DEXA scanner) can tell you your BF%, and attractiveness will typically correlate with BF%, but ultimately your "customers" (romantic partners and targets) decide how attractive you are. Not a perfect analogy (priority is still something you'd decide internally, not your customers directly), but hope that clarifies things.