I think about this from time to time. Not so much "greatness," but excelling in my profession. I work in a semi-creative profession, and most of my colleagues and mentors take their work home with them every night. I'm used to getting e-mails with ideas at all hours, and there's a big emphasis on what you can accomplish away from the keyboard.
RPGs work much the same way. I only play 4 or 5 hours a week (which, I imagine, is a lot for an adult with a profession), plus an hour or two more writing out notes or maps for my sessions when I DM, but, as a DM, I'm thinking about the game all the time, looking for ideas to bring to upcoming sessions. D&D occupies a lot of my creative headspace. I sometimes worry that having that creative distraction keeps me from focusing on my work and making big creative jumps at my job.
On the other hand, I've found that, when I really need to turn on the juice at work, I have no trouble prioritizing. It's a bit of a pattern — when things get slow on a project, or in between projects, I get creatively bored and start cooking up all sorts of campaign and adventure ideas, and push for my turn at the DM's chair (we rotate.) By the time I run my first session, I've started a new project, and all my creative energy gets dumped back into that, and my campaigns tend to fizzle once I run through the notes I managed to prep in between. And that's fine.
That's what's great about hobbies. They are much more rewarding than most jobs, and we only need to put as much into them as we can. If my group stops being rewarding, I can drop out. I can step away for a month because of work pressure, or ask to play every other week, or ask to switch to a different game world or style. In my profession, I have to put in the slog as well as the creative elements. I can't just walk away from a job every few months because it's not meeting my needs. Sometimes it is mind numbingly boring, and that's when my hobby sustains me, because I can be imagining adventures while I'm doing work that somebody should have gotten around to designing a robot to do. It's great creative practice, because I constantly have to generate ideas, trot them out in front of others, listen, revise, react on my feet to others' ideas, etc.