I have not always been a good DM. I think it might still be presumptive to call myself a good DM and that I would be more comfortable saying I’m a decent DM with a few specialities, but I think I wouldn’t argue against anyone if they called me a good DM. I think the lesson I learned that made me an alright DM was to never, under any circumstance, take away player agency. They’re free to do whatever they want in the game and I should support their endeavors, but they’re also free to suffer the consequences of their actions.