So many of us go above and beyond for our companies/projects/teams/whatever. The author here describes overcommitting at work. We might have the best of intentions, but at some point, we don't see the returns we yearned for and start to question what all this self-sacrificial giving is for. That is when burnout really sets in. I've had friends burn out while working for hostile or indifferent managers, startups that are trending the wrong direction, companies that engage in illegal or unethical behavior, etc.
A second insight was that burnout can play a positive role in our lives. It's like a circuit breaker that trips to protect us from a damaging situation. When we feel burnout coming on, it's a warning to pay attention to an important misalignment in our lives.