psychology student here - this is actually a genuine therapy strategy! It's called Behavioral Activation, it's been proven to work on par with medication and it's a branch within CBT. it's based on just what you said here - the more you do, the better you feel and the more you do!
It's about getting yourself to start with the small things, with doing something nice, like eating your favorite cookies for breakfast if you know you're struggling with cooking, watching that movie you like even if you've seen it a hundred times and you're watching it in bed on your phone and that's the only thing you do all day, using some mouthwash if you know you haven't brushed your teeth in a week, maybe calling a friend you haven't had the energy to meet for months even if for 5 minutes or just texting them a meme, walking a couple laps around your room if you struggle with going outside. It's really all about whatever you can actually manage to do - and while all these at first seem like "not much" and kinda pointless because they're not "real progress" to outside people and it's tempting to just discard them as unproductive because you're "supposed to be doing it differently" like eating healthy food and getting out and meeting people, they actually achieve a much more important goal with depression - they get you to feel nice for a moment. They get you to feel like you've achieved something, even if it's small. It's progress. And if you've achieved one thing, did one small step, then maybe you can do the next one - and another. and another. and one more. and slowly, very slowly, you start doing more. you eat a cookie and maybe make one meal a day, you go out to take the trash and maybe even sit outside for a couple minutes, you brush your teeth every now and then, you play a game with that friend you've missed. it's, hard to see as progress at first, but it really is. depression is a beast and it's horrible and enormous and larger than life and feels like you can never get out from it - which is why the small things matter so incredibly much
and of course, it also works in reverse - if you feel like you haven't achieved or done anything lately, then you're more likely to have less motivation and energy and do even less and so sleep in longer and do even less and then avoid more and do less and avoid and that just keeps on going, and it's a vicious cycle to break out from
which is why with BA, and I cannot emphasize it enough, the tasks have to be easy and rewarding. they have to be things that are both within your reach, and that make you feel good. they could be things like clean your room or do dishes or do homework because that does give satisfaction, but setting those as the means misses the point - you're already depressed, how likely are you to have motivation to do things that you're already struggling with? they should be the result, not the expectation. first, do the things that feel nice. start gradual. build it up. depression is hard, and defeating it means you have to steadily sneak up on it, even if it means going slow
so go, brush your teeth. or eat a cookie. or two. or three. do one small thing, whatever you want. it's not a cure to depression, and it's not meant to be. but it might just get you to feel nice for a moment, and that's the first step to recovery
