I haven't played anything since Witcher 3 and I rather see my fatigue growing in this field. : ) I can only turn on a new game to appreciate some technical aspects and then instantly get this ineluctable pop in my head warning about wasting my time. On the other hand, I am quite the opposite of "disciplined" and I am genuinely wasting hours on ineffective indolence (I guess it doesn't switch that pop on).
But to answer your question about the source of my drive:
Firstly, I don't think that my commercial commissions are satisfying enough in terms of creativity. They are often rushed, with hectic deadlines, and require a lot of mediocre design work. I cannot complain but I would easily get burnt off if not for my personal projects. It's also not that long since I decided I would like to focus totally on arch-viz and I just need to craft my career a bit into that direction since my client base is at the moment pretty random, spanning from vfx industry to advertisement.
Secondly, I have some constantly insatiate hunger for it. I get inspired a lot on a daily basis and my head is crowded with unrealized ideas. Making them come to life is still one of my biggest joys. I have also this kind of affliction that makes me really positive about the stuff I am currently working on and really negative as soon as it's finished. It may not sound that great but it really pushes me forward.
On the other hand, I am pretty impatient and try to work smart and fast. I buy, re-use, adapt, fake as much as possible, which is not my preference at all but I have learned to accept it. I look with some hints of envy at artists that create their intricate works entirely with their own hands in every crazy detail.
I must also admit in the end that I probably just work too much and it'd be much healthier if I did less. : )