No i think the majority of cases are simply longtern unhappiness with something. A lot may tend to set goals, these may never get fulfilled, causing depression, someone else can become depressed by so many triggers.
For me, I have quite a purpose in life, but I've been depressed without cause since i was a child. Such of this depression is long term, lacking motivation, having no appitite, mood swings etc. Diagnosed major depressed with hypomanic features.
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"When you begin to realize your own existence and break out of the social norm, then others know you have completely lost your mind." -PerfectlyDarkTails
AS 168/200, NT: 20/ 200, AQ=45 EQ=15, SQ=78, IQ=135