Optimism for one thing. Non-depressive people usually think their problems are conquerable and they can find some enjoyment here and there.
For another, the perception/prediction of effort is very much different. In a depressive episode patients will estimate all tasks as fundamentally harder, leading to huge problems in motivation and making decisions. It's quite analogous to how increased gravity on another planet would affect your movements and decisions about your movements.
When the capacity for enjoyment or positive emotions is reduced, you won't be seeking enjoyment as much. Which is a vicious cycle, of course.
So yes, depressive symptoms are a big hindrance, even if you have other big problems, none of which I would want to diminish.
My therapist also tries to explain the difference between a “depressing” thought and a “depressive” thought. The first is just sad: “my ex started dating my roommate and that makes me feel uncomfortable”. The latter snowballs into morbid or hyperbolic predictions of the future: “now I’m going to be ostracized from my social group because they won’t want me making things weird. I also work with him and my professional life is going to fall apart. Ill have no safe space and I’m going to crack & burn all bridges i have here. I’m going to need to restart my life somewhere across the country”
Another comparison would be those trait controllers they had in Westworld. The writers/engineers could move sliders on a flexible sheet for different character traits.
In depressive episodes the sliders for "optimism", "motivation", "thrill seeking", "social behavior" would be significantly lower than they are normally.
But the idea that those traits are not constant goes much against our cultural programming, I think.
The language around this is messy because not all depressive symptoms are shared, but I would say it's in how you view it.
In your example, being single and having a lot of debt can change over time. But if you were in the throes of a depressive episode, then you might believe absolutely that neither of them can ever change because they haven't changed yet/they'll take so long/it's impossible for you to expend the effort needed to change them/[...].
The facts are the same, but the conclusions you draw are different.
2) your ability to seek help to cope with it would chang
3) your perception of time is often different during an acute suicidal episode - time stretches out which makes this particular moment feel all-encompassing.
Put another way, even if I wasn’t depressed, I’d still be single, diabetic and have a ton of debt. What about that would change?