I think it’s usually a mistake to relate “will” too strongly with “power”. “Try harder” doesn’t usually accomplish much. We generally tend to get obsessed about certain problems that bother us, but I’m not so sure it isn’t the obsession itself that isn’t the biggest problem. For instance, it is the obsession that makes me fixate on some aspect of my behavior that I don’t like, that I want to change so badly. But that obsession limits the resources available to me by concentrating my attention on one overt pattern of behavior only - when there are so many aspects of myself (beliefs, “other” habits, etc.) that come together to create that particular pattern.
I’ve found this book helpful when it comes to these kinds of things. Of course by “this book” I mean taking the philosophy to heart, and actually undertaking the practices. Of course if you’re depressed you may find it harder to actually undertake the practices (because you’re too depressed to bother), but a little inspiration can combine with a litle practice and the practice itself is inspiring… and before you know it you may actually pull yourself up by your own bootstraps. We can let the determinists worry about out how it all works.
Of course you can just be depressed. You can just feel what it’s like to be depressed and get to know it a little better. I don’t mean wallow in it though - I mean pay attention to it, discover its patterns, notice what other factors feed it or inhibit it… really get a feel for it. I think depression is made worse by trying too hard to avoid it. That is the basic vicious cycle - it is often the case that the attempt to avoid some discomfort, contrary to our deep-seated beliefs, in fact empowers that discomfort.