I started working on a long-term project 1.5 years ago. It's in cryptocurrency. People in crypto would call it a shitcoin project. Up until now, it's a solo project. I'm the only person working on it. Not much outside interest. But I learn some things along the way.
When you think about the expected or probable ROI, you'd likely give up. These projects or ideas will likely fail. You have less than 1% chance of success. You're trying to calculate the extreme tail risk. It's not worth the time to think about it. The process is demoralizing.
One trait that I found useful for these long-term ideas: curiosity. If you're curious about something, you can do it for a long time. You still do it even when you know it would likely fail. During the process, you can learn things that are not exactly applicable for your idea. But they are useful for your learning.
Another aspect to think about is to find the failure criteria. You can decide when your long-term idea is invalid. When you see X happens, you know X would invalidate your idea. X is the correct idea, your idea is incorrect. At that point, you can stop.
An example: I have a hypothesis that battery electric cars may not be the future. I work on alternative ideas. A failure criteria for my idea: When battery electric cars have more than 50% market share. This example illustrates the unpopularity of working on long-term ideas. People would call you stupid. You'll likely fail. Curiosity is the only thing that keeps you going.