My friends had a company. Then they got into EverQuest. I don't know what percent of "work time" they spent playing. Maybe zero. But, they would stay at the office after work to play. I visited one day and saw playtime in the corner of the screen of one friend at ~36 days. My first thought was "what could they have done with over 5 months of "work time". If you work 40 hours a week then 36 days of game time = 846hrs = 21.6 weeks = ~5 months or work. Note: I use tons of time in my own life in ways that others would not (like spending time on HN) so again, not judging, just obsverving, though I often wish I did more productive things that would / would have lead to more future freedom.
In any case, one of those friends encouraged me to give it a try saying it reminded them of when we used to play D&D in high-school. That friend had also spent time becoming a fletcher (maker of arrows). If I understand correctly, the ability to make bows and arrows from materials was a skill. You gathered the materials, then picked "make" and you had a random and relatively low chance of succeeding. If you did succeed though, your "skill" at making bows and arrows increased. Once you passed some threshold you could always succeed. This made you a "fletcher" and people who needed bows and arrows would seek you out to buy them from you. I thought it was amazing that my friend effectively had a 2nd job. I'm guessing that's common a game mechanic in games since then?
Another of those friends also played at home on top of at the office even though they had a spouse and 3 kids under 10. After a while, their spouse demanded they stop. They visibly deleted their character but then made a new one back at work and of course all the "overtime" for the last several months had actually been "game time". 3 months later the spouse found out and said "quit or I'm leaving". My friend quit.
When World of Warcraft came out and blew past EverQuest in its reach that friend told me if I wanted to check it out be sure not to make any friends or join any guilds. They said it's the social obligation that's the addiction. Like joining a sports team, if you're not there your group can't achieve their goals so you feel obligated to participate and that's the addiction. I've never tried WoW either, having seen people spend so much time in it.
Also another random thing, another aquaintaince moved to Thailand and setup an EverQuest farm for a year or two which at the time was a new thing, making a living selling stuff in game. In which games is that common now?