I hear other players talking about them. There are a lot of little things in the game that are semi-passive and fully-passive income generators. Things like Planetary Interaction, running your own POS (i.e. BPO copying, Invention), mining, industry/building, and R&D agents.
Over time, I've marked many of these off the list. A couple years back, I was a mission runner (and sometimes Incursion runner) and I thought "I should set up some PI, it won't take long and it's passive income." So I did, and I ended up hauling once or twice a week.
A little bit after that I said "Wow, I still own all these capship BPOs and stuff; I should set up a POS so I can fire up the copy printer." So I did, and I ended up hauling fuel, or jumping back to manage the output of the process once or twice a week.
For awhile, I was doing a bit of mining, and was using the output to fuel a factory. By filtering the mining yield through one of my capship component part BPOs and selling the resulting parts, I could add on 3-10% on my mining yield for very little work. But I still had to go buy the higher end minerals to fill out each order, so I ended up hauling mega and zyd here and there.
I'd like to say that this entire empire ran itself and I loved every minute of it.
But no, I was quite an idiot about this. The PI system I chose was different than the POS system which was different than my mining/building system. Each system was chosen for various reasons (moon PI composition, proximity to ice belts, number of asteroid belts, proximity to trade hub, proximity to 0.4 space, etc.) but it was horrible from a comprehensive point of view. Very quickly I'd log in each night, realize I had a chore to take care of, find a different ship, make 6-20 jumps in a slow Impel or Orca, and once done I'd need to logoff instead of completing the instead of the mission or joining the Incursion I'd wanted to do.
EVE had become a job. I was making decent isk for very little time logged in, but I was locked into a schedule. It was a monster of my own creation, sure, but was still a monster.
I write about it because I'm still amazed how easily the chores list sneaked up on me. Each addition was small, but the total impact to my play time was huge.
This went on for a few months, and then the POS came down and the PI went untended. I briefly considered consolidating my operations (duh) but I was tired of the whole "chores" aspect of it all and went off to find some red icons to shoot instead. If real life ever settles down (haha) maybe I can try again and make it work. Until then, I'll intentionally keep my schedule free.