I'm going to fully explain my strategy, here, just in case there are others struggling like I am. I have mild ADD, which might just be a natural side effect of being on the autistic spectrum. I have Asperger Syndrome. I'm just like any normal person except that I don't socialize super well, and I tend to have very narrow and inter-related interests. But there's an underlying big problem. I lose interest in what I'm doing if it doesn't change up. This is why I can't work normal jobs. Doing the same thing over and over, day after day wears on my mind and spirit so much that it causes me to go into a state of constant and building anxiety which doesn't go away just getting a weekend break. Hell, I don't even try to have a daily routine or daily schedule. I eat when I feel like it, I sleep when I feel like it, I work when I feel like it, and break when I feel like it.
Sometimes I'll inch my sleeping schedule along until I'm going to bed mid-day and waking up at the stroke of midnight. I don't have an alarm clock. I don't even have a clock. I tell time with my computer or my phone, and hardly keep track of the passage of time or hours worked.
I used to have a schedule and routine back when I was in school, and I hated it. It didn't really start wearing on me until I was in high school, though, which I think was a gradual wearing off of my ability to just do the same things over and over as a child. And it was finally gone by 10th grade. The last few years of school were a nightmare.
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It's the same when it comes to developing video games. I couldn't get through them, so I had to develop a strategy to beat it. How it works is simple. In a nutshell: I work in an as-needed basis.
Back in 2005-2008 I was messing around with RPGMaker 2003, and made a game. It was the first game I'd ever finished (this had nothing to do with my autism and everything to do with my teen depression) and it would be 1 of 3 awful games I finished before falling into a very long rut. In 2010 I managed to complete 2 more quick games, then decided I wanted to stop with the quick, short, simple games and move on to something more advanced. I haven't managed to complete a game since.
Recently I realized I had somehow fallen into a routine: All the art first. It all has to be there. Then all the base engine coding next. Then all the game play elements. Then all the level design. Somehow, when I decided I would be come more serious, I got it in my head that this is what I needed to do. I would work in strict steps that ultimately lead to me getting tired of the monotony of the project and grow to resent working on it. I would subconsciously start feeling trapped by that project, and my mind would wander to greener pastures: other games I could be doing instead. And at that point, the damage was irreversible. Abandoning the project was inevitable from that point. All projects began under that model are doomed from the start.
This is something I never meant to happen, but would always inevitably be the fate of every game I worked on. (Well, almost every game. Some fell due to a lack of experience.)
After dropping my last project I started working on the cover art of my novel. I had an entire month to get excited for a new project I was starting on while I drew, but the problem still loomed over me. Was I doomed to just struggle with this curse and never get anywhere? Sure, maybe there's a way to medicate it. But I knew I was stronger than that. I had done it before, after all. But how?
And that's when I started to analyze the way I worked on the games I managed to actually get through. Two of them were short and simple, and didn't require a long work time, but the first one wasn't as short. It was short for an RPG, but I worked on it for months. And that's how I figured it out, I think.
When I worked, back then, I worked as mentioned above: in an as-needed basis. Included with RPGMaker are default assets. I used mostly those, so I was just able to start in on it by designing a level for the start of the game. Rather than trying to fully hash out every level in the game, I went through it one at a time. I'd design the level, add the events, then work the story if it applied to that room, then I'd move on to the next area. Or if it were a building/dungeon with multiple rooms, I'd chose the next room I would do and start on it. If I came across something I needed for an area I would stop, open up my image editor, and create the asset I required, add it to the area, and go back to it. I had the opening of the game finished long before I'd even thought about what the world map would be like.
All of the monsters, or at least 99.9% of monsters, were custom. I think only a handful of them were just character battle sprites used as monsters.
I designed a few low level monsters, and set them up, created the world map, then test-battled the monsters. Any time I created a new region that required a rise in difficulty, I would stop, design a new monster or two, set them up, test them, then give them abilities. Most of the skills in the game were custom, too, so sometimes I could design a new skill for a character or monster, animate it, and test it out.
As you can see, I never had to do the same thing more than a time or two in a row before getting to do something else for a while. Then I could move back to doing the previous thing and it wouldn't seem dull to me. I have a feeling that's what allowed me to get through it. The entire game was improv, start to finish. I did whatever I wanted (Within reason. I'm not going to add something that doesn't fit just because I want it there), usually only when I needed it, and was allowed to switch tasks so nothing got all that monotonous. I had a kind of direction I wanted it to go in, then I made it up as I went. Sure, the game ended up a boring, repetitive, grindfest that could probably be completed in 3-4 hours or less, but that could be blamed on lack of experience, because I was highly inexperienced back then.
In the event that I did start to tire on the same project, I would move to other RPGs I was working on at the time. Not a single one of those has been released due to being purely awful and of irredeemable quality, but working on them did help take the edge off my main project from time to time.
I can't tell you if going back to this method has worked out for me, because I'm only still just trying it out for the first time in 6 years, but so far so good. I'll keep note of how things progress as I work this strategy out in real time.