It's not just a thief, though. I mean, yes, it will rob you of a significant amount, don't get me wrong. The actual action of theft occurs - but to call it a thief binds it to just one archetype, gives it just one shape.
That just isn't the case.
Some days it is just a cloud. It sits up in the sky and on occasion overcasts the sun, but it is a distant thing - inescapable but not terribly pressing. The cloud might even make everything look a little more picturesque, when it moves its ass out of the way and lets the sunshine through.
Some days it is a weight. A singular weight, that sits atop a subject or topic or thought, and pins it down, makes it hard to move. It means that shifting it from inbox to outbox, mentally speaking, difficult. You spend that much longer just hauling at it or struggling with it, even something that you frustratingly realise should be simple. It can create an aversion, quite easily.
Some days it is the black dog, that Churchill and others have famously described it as. This, too, can take different forms. Sometimes the dog just follows you, all day, hoping for your attention and slightly getting in your way. Anyone who has had a slightly elderly Labrador probably knows how this works.
Some days, however, it is a different kind of canine. It's a wolf. A predator. It stalks you. It doesn't generate gentle frustration - it causes fear, and it's a fear that doesn't come good until later. It makes the shadows longer, and even if the thing you are engaging in is brightly-lit and pleasant, you just know it is out there - waiting for the moment your guard is down.
Some days it takes the form of blinkers. You need to do X, Y and Z, and you quietly thank your depression for not getting in the way of that - but it blanks out the rest of the world. Pausing to look around isn't an option, because the only task that exists is directly in front of you, and there's no other people in this world; only the one you have to talk to at that moment.
Some days, it is the ocean. It is either a massive inescapably looming presence, an infinite icy depth that is always there at the end of the land - or it is something you are under, an immense pressure on every point of your being, just pushing down, down, below the thermal layer and away from light and warmth.
As of right now, I have witnessed a whole new shape; and that shape is barbed wire.
It's like a knot of barbed wire, tangled around everything. It is perhaps informed in shape by my chronic pain issues, but either way - it's like every motion, every twist, every turn, just gets more and more tangled up in the ripping, tearing wire. The more one struggles - the worse it gets.
It also makes it hard to see. At a distance, barbed wire is difficult to spot - it defies examination, and even up close, even when one can understand that it is indeed barbed wire, actually untangling or unwrapping it seems like a Herculean task. Where would you even start?
It's a trick.
In Pacific Rim, Raleigh Becket advises Mako Mori to not chase the rabbit. Depression is its own rabbit. It wants you to chase, to delve, to study - but not with an eye to fix, to solve, to make better or understand. Depression is a self-replicating Von Neumann probe of a sensation, that seeks to break through into every aspect of what you are doing, and the barbed wire Gordian Knot is just one example of how.
You can't do what Alexander famously did and just cut it. That isn't an option. The best way to deal with the barbed wire is to just try and do what you normally would. Get things done. Not ignore it - it's impossible to ignore - but to look at it, and grunt, and shrug, and get your shit done anyway. It's not going away if you pay it attention, nor if you ignore it; but if you can get into the groove of how you do things, of how life works for you when you aren't entangled, you weaken its hold on you.
It's not a demon you can slay with a sword. This is a demon that requires diplomacy, and tenacity, and fortitude.
I wish anyone fighting this demon all the diplomacy, tenacity and fortitude they need.