There's a study out there that says that people who are incompetent don't know it, and often think they are better than people who are competent.
Thus, knowing you're a bad GM may be impossible for some people.
It also turns out, that competent people are more likely to rate themselves lower in skill, compared to others.
This might be seen as modesty, but it's more likely that competent people think they're average, and that most people know what they know. Which, as it turns out, most people are stupid (when you're smarter than average, half the people you meet are dumb).
Thus, knowing you're a bad GM may be impossible for some people.
It also turns out, that competent people are more likely to rate themselves lower in skill, compared to others.
This might be seen as modesty, but it's more likely that competent people think they're average, and that most people know what they know. Which, as it turns out, most people are stupid (when you're smarter than average, half the people you meet are dumb).