As many have noted, depression is very difficult to describe even after going through it yourself; it's one of those omnipresent and overbearing sensations, always there but never really distinct. For myself, it mostly manifested as extended bouts of apathy and indifference; I didn't want to do anything, often choosing to do whatever made me feel somewhat content and aided to pass the time most efficiently. Episodes of sadness weren't uncommon, but not a huge aspect; melancholy was definitely present.
While MMORPG addiction/compulsion/whatever isn't really the topic of debate, I can safely say that it can be a fairly strong indicator of someone having more severe mental issues; a depressed person can easily find themselves lost in these virtual worlds, as they provide a steady stream of mild enjoyment and are better time-sinks than they probably should be permitted to be.
Anyhow, I often found myself saying the words:
"I can do anything I want... but I don't want to do anything."
At the time, I would mostly attribute it to general laziness... but having gotten over my depressed state, I find motivating myself to be much easier. I can't quite explain why, as it's not because finding reasons to do things is a problem; I simply want to do something, plain and simple.
---
Explaining to someone who hasn't had a similar experience with depression is especially difficult, it's just too foreign a concept to grasp. As noted above, I don't need a reason or incentive for me to do something these days; other than indulging in some rest & relaxation, it's fairly normal for a person to want to do something. A depressed person doesn't have the luxury of wanting to do something for the sake of doing it, for whatever reason.
To go somewhat on a tangent, looking into the anime series
Neon Genesis Evangelion might be not be a bad idea. While it's not quite obvious on the surface, the series could definitely qualify as a case-study on depression in general; the series was (in)famously born out of the creator's own battle with depression, and it doesn't pull any punches. I've also found it tends to strike a chord with those who are familiar with depression, whereas those who aren't... well, the series divisive reputation exists for a reason.
---
Quiet Stranger said:
My next question is what kind of barriers arose for you when you had depression? What impeded you from curing it?
Again, it's mostly about motivation.
The short term approach of working on immediate goals can help one be more productive, but that can easily become little more than a coping mechanism rather than helping one work towards an actual solution. As noted with MMORPGs creating problematic habits, they do this approach a little too effectively.
Confronting the depression itself (even if indirectly) is more or less what it comes down to, but it's still difficult to do; apart from being tough to pin down any one cause for it, and the individual has to be motivated to do something about it themselves. The last part is probably the most critical, the depressed person needs to want to get out of it; if not, any effort will be hollow and temporary at best. For someone to get out of a depression, they have to take a genuine interest in something. Oddly enough, for myself it ended up being my studies; structural engineering design to be specific, which ended up being both the most demanding of my courses but also the most engaging. Nevertheless, it's important to note that
this is only the start of recovering from depression.
The phrase "vicious cycle" is often applied in a negative context, but it would be more apt to call it a "cycle of reinforcement"; it goes in both directions, believe it or not. Depression is one such cycle, people get down and "stuck in a rut"
because they're down and "stuck in a rut". Apathy plays a huge role in depression, and to get out of it is to not be apathetic; obviously easier said than done, but it's the honest truth. Because it's a self-perpetuating cycle, it's rather difficult to halt; still, it has to be done.
Back to recovering from depression, taking an genuine interest in something is the place to start. Because they're really getting to the topic, they'll almost certainly be doing reasonably well (or at least showing signs of progress); this will provide a boost to one's confidence, giving them the motivation to carry on with the interest. This will start carrying over into other areas in life, building more confidence in the aforementioned "cycle of reinforcement" and providing more self-motivation. And yes, this is also a self-perpetuating cycle; once it's rolling, (formerly) depressed individuals will find it easier to carry on feeling better about themselves and what they do. Incidentally, this is also why depression can be so difficult to explain to those who haven't gone through it before; you simply don't know what it's like to be down that low until you get there yourself, nor do you really understand the difficulties of getting out of it.
---
Hope that helps, but that's my take on the subject. Best of luck.