It can be. What about if when you are small someone does something to you that is horrible. Because you are so small that you don't know how to react (an adult would probably get angry and tell the horrible person where to go !) when it happens.
You (not being aware of this at the time, if ever) think its about you and begin to feel there is something hateful about yourself.
Anger which should have gone to the horrible person has twisted round and landed on you. Anger/hatred of yourself gets rooted in your brain which leads to depression.
This is one of my views on longer term depression (like mine) but could apply whenever a person can't show their anger at its target - it has to go somewhere and turns to the familiar self hatred.
Anger and hate are cut from the same cloth, I think.

Hope thats not too much of a jumble - took a lot out of me to do that -phew !

Poppet