One of my root causes was a poor self-image. I never was able to live up to his expectations. I remember one time after my second marriage he was over to the house and I showed him some shelves I built. His only comment was "they're crooked." Not helpful.
As my personality developed, I realized I wasn't good a "guy" things. I wasn't mechanically inclined, wasn't good a building things, not good with my hands. I felt unworthy because, that I wasn't much of a man. My experience with my first marriage only intensified that feeling. My first female boss at work didn't help either.
I eventually realized I didn't have to be a stereotypical male to be a man, but it took a while.
Then I had a strong-willed child, then married a strong-willed woman. I realized I didn't have the wherewithal to cope with strong-willed people.
At work, they only frustrated me and made me angry - and I'm convinced that's one of the reasons I wasn't promoted as others were.
At home, I found it easier to just let them do whatever hell they wanted to - but of course that didn't work. I would put up with things so long then would explode in frustration. And honestly, I still don't know how to cope with them.
Still, knowing the root causes of my depression helps my ability to cope with life in general.