Sometimes negative emotional responses are appropriate and even though they cause bad short-term side effects, those side-effects are worthwhile because the negative emotion is a physiological response to an intolerable situation or circumstance, exogenous to your self or attitude, that must be avoided or changed.
The trouble comes when a person gets embedded into a circumstance that truly, legitimately warrants the negative emotion, but which is not (or cannot be) removed or changed.
Crucially, it is a situation for which it is unequivocally correct to bear the costs of negative short-term emotions to create a noticeable signal that something's just not right and something needs to be fixed. But where those negative emotions would normally serve their purpose and direct you to make a change or direct someone else to make a change in response to you, instead no change occurs.
Now the supposedly short-term effects of the negative emotions become long-term effects, and that is what burnout is. It's the application of negative emotions in a circumstance that literally requires short term change, but which resists being changed over a long period. The circumstance is the burnout. Not your negative emotions, which are merely the correct and reasonable response to the circumstance.
Problems with a job are a classic example. If you are being treated badly, if basic human needs are not being met, or if you are actively being prevented from satisfying basic human drives, that absolutely warrants negative emotions, and their short-term downsides are necessary evils to bring about change to your situation (whether change that you are able to enact, or if you are not in control, then change which someone else must enact).
But at the same time, modern employment is structured for most people to be engineered precisely to disregard human negative reactions. Such reactions will be vilified and/or punished, but they will not be considered in the fullness of humanity and accepted as signals that something is wrong and in need of adjustment. It's simply incompatible with most implementations of bureaucracy to allow for something as messy and bespoke as human needs to drive business policy, and this is why we require employment laws to enforce at least a minimal degree of human-needs-respecting policy (apart from extremely rare businesses actually run by people who consider the human condition of their workers), and also why political activism around worker rights has had such a bloody history, and shows no real reasons to believe it's going to be less bloody going forward from here.
So it's a perfect storm. Jobs generally trigger negative emotions due to the way that jobs prevent humans from satisfying basic, required needs (needs for privacy, needs for autonomy, etc.). But our prevailing framework for structuring the human-to-work interface, bureaucracy, is literally based upon the idea of only accommodating human needs to the most threadbare level of uniformity and minimality.
As a result, to last a long time in a company, you either are already or become one of the following:
(1) genetically predisposed to be capable of sublimating away the human needs that will go unmet, thus sublimating away any negative emotion reactions. Some fraction of this group may not be genetically well-suited for it, but is instead well suited to "drink the Kool-Aid" and fundamentally re-map their internal goal orientation to pulsate in unison with their employer [either way, this is extremely rare, and leads to what Michael O. Church called "macho subordination" whereby people compete to be seen as the "most loyal" by virtue of who can overtly signal that they are most willing to sublimate away human needs for the sake of the company, similar to a proud martyr kind of attitude]
(2) constantly drenching yourself in stress hormones, probably eating your feelings, failing at personal relationships, exercise goals, etc., and slowly decaying into a burnt out mess because you can barely duct tape it all together in the morning and drag yourself to face the sisyphean task of pretending to sublimate away your negative emotions every day [pretty common, maybe not the majority]
(3) taking medication / seeking major therapy which helps mask the symptom (the negative emotions) without addressing the actual cause (that the concept of work life is structured to be at odds with human goal satisfaction) [probably a much larger fraction than we admit]
(4) someone who thinks they are "getting by" but who is actually acting horribly to their coworkers as little cracks in the facade start showing over the years of dealing with the negative emotions, rendering you into someone who is probably the cause of this whole chain of problems for other people, especially when you rise to the level of manager [most middle management that I've ever heard of, encountered myself, or read about in principled research on this issue, like Moral Mazes].
I suspect that many other modalities of life -- long term resentment in marriages or relationships, family dysfunction, negligence regarding easily preventable health problems, etc., -- can be analyzed in a similar way as working life is analyzed above, and that problems of burnout affect most of us in huge ways across vast spectra of our lives.
As this becomes better understood, I think burnout will begin to be seen as a fundamentally physiological and even rational response to the way that most modern modalities of life are structured.
But I also predict that the only change is that research into pharmaceutical engineering to prevent burnout symptoms will intensify, and that lazy mental health professionals will mostly resort to tossing drugs at people to get them off their back, and basically, with regard to burnout in general, the prevailing attitude will sort of just be "deal with it -- take some drugs to alleviate the symptoms, but don't expect anyone to ever care about the cause."
This is one common theme I have seen in a wide range of dystopian literature as well, even though it's not always directly stated as such. When side-effects of structuring society in fundamentally anti-human ways become problematic and it eventually starts trickling up to rich people who begin to be inconvenienced by it, the response is to create a distraction or a device or drug to mask the symptoms just long enough for symptom-sufferers to go on servicing that rich person's desires, but none of which actually offers relief from the underlying cause, and it leads to wider and wider spread feelings of prolonged misery and burnout, despite greater and greater societal wealth in the form of technology.