Robin Williams dead. So very sad. Dead by suicide? That's a whole new level of unfortunate.
I think the problem most people have understanding depression is that they have a view of "self" as an independent entity and "brain dysfunction" as an external agent. But once you've got brain dysfunction for whatever reason, it BECOMES part of self. You can't stand outside it and try to reason your way out of it because it literally IS part of you. There's no distinct depression-free "you" anymore that one can address.
What's an analogy? How about this? People like to view depression as if it's frosting on a cupcake. You can remove the frosting and not affect the cupcake. The cupcake is always itself, simply adorned or unadorned.
But depression is more like paint. You have your normal cheerful yellow self and some blue depression is added. You're no longer yellow. You're green. And you're not going to be able to find your old yellow self anymore; it simply isn't there. Removing the blue isn't in any way easily done and may be impossible to do. All one can try to do is learn to live with green and see the positive in a world in which green is your new color.
Or so it seems to me. Happily, although I have my cyclical ups and downs, they are nothing anywhere near as extreme as it seems Mr. Williams was dealing with. His family has my sincere sympathy.