I think what the authors are getting at is that many failure conditions are more likely to manifest under load. This includes various kinds of resource exhausti

I think what the authors are getting at is that many failure conditions are more likely to manifest under load. This includes various kinds of resource exhaustion, including those induced by leaks. It also includes things like timeouts due to long queues, and even race conditions. The higher the load, or the longer it's sustained, the more likely it becomes that such bugs will manifest. In every such system I've seen, from very early days of the internet or old-school HA to modern multi-thousand-machine clusters, there have been bugs that only showed up under heavy and/or sustained load. Both Erlang's supervisor trees and Recovery Oriented Computing (Berkeley/Stanford) are based on the observation that such failures will always be with us, and have influenced many subsequent systems - arguably including CockroachDB.