I agree with you, no one can really know what haunts a person affected by depression except the person himself/herself. I think my statements were biased by my own experience with this cancer I had some years ago (and by the fact that I don't really like psychologists, but that's just another bias of mine
), I apologize for that.
Nonetheless, even though seeking professional help should be the main course of action, I think that for a fair part of people (especially the youngsters) who struggle with depression, asking directly for help is as difficult as trying to overcome depression itself, because it would require for them to fully come to terms with the fact that they are, in fact, ill, which is a thing that, in my opinion, a depressed person just doesn't have the strenght to realize, or the will to.
I think that, in this case, taking some time for yourself to fully understand what is (are) the real problem(s) that prevent you from living life to the fullest, while deepening few but significant bonds with people you trust to allow yourself to remain afloat at least for the time this process takes, is a good starting point (at least that was what helped me at the time). Whether these people are to be fully trusted or completely inept at taking up the task, that is an other matter.
That's just my two cents anyway, please do feel free to reply.