[wnkrshm]

Disclaimer: I'm not a doctor but I've had diagnosed work-related depression ('burnout') and got treated for it. This is based solely on my personal experience:

You don't need to work hard to be burnt out, you may just be continuously confronted with tasks or conditions that are too much for you to deal with. A high stress environment. Burnout is just another word for depression, caused by a specific set of circumstances that are usually work/career-related.

Your son may have clinical depression, you can't willpower yourself out of one of those.