Look at it the other way around - you could have a different outage every single day and as long as that outage only impacted 4.3m users and they were different users each day, it would look like a once-a-year event to the average user.

They’re saying there’s a lot of leeway to break things (in a small way) at scale.

No guarantees, but a feature flag or canary deploy can significantly increase likelihood of impacting a targeted subset of users.