The boss, not the workload, causes workplace depression
To elaborate, the things that often lead to unhappy workers also include:<p><pre><code>  - Unknown expectations from the job
  - Little or no control over decisions that affect your job
  - Missing feeling of involvement
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The fair treatment bit is mentioned in the article.  The reality is that people tend to be more irrational than they probably ought to be which usually has significant (negative) side-effects.