hawkeyefan
Legend
Trust in self, mostly; and a sense of doing what's good for one's own game in both the short term and the long.
Difference of perspective.
In general, the player's first focus is on the success of their PC (and somtimes, of the party) and on the immediate here-and-now elements that go into as best as possible ensuring that success. The player has much less impetus to do anything on a bigger scale to ensure the game itself keeps going any longer than maybe the next few sessions, and can (and IME almost universally does) leave that up to the DM. By the same token, it's hard (though, sadly, not impossible) for a single player to do something that sinks the whole game.
The DM, meanwhile, not only has to focus on the immediate here-and-now run of play in order to keep the game going right now but also has to focus on the long term and think of what will keep the game going for the next one or two or fifteen years, assuming that's her intent. What this means is that, because a DM can sink a game far more easily than can a player, she has to be able to trust herself not to do something that would sink it. And so, even though any DM has infinite dragons and infinite falling rocks to throw at the party the wise DM knows it's in her best interests not to use them, making this often-used example really nothing but hyperbole.
Do you solely GM? When you play, do your instincts about what makes up a reasonably balanced yet challenging game vanish? Aren't many players also GMs and vice versa? Is it a quality of the role in the game that causes the phenomenon, or is it a quality of the person?
I GM quite a lot, but I also play. I don't tend to look at the games I play in as somehow less "mine". I'm responsible for how those games go. I'm not solely responsible. But I'm not solely responsible for how the games I GM go, either.
Perhaps it's the sharing of responsibility for the game that makes players less likely to scramble for every competitive advantage? Perhaps withholding the ability to have input on the game makes folks desperate for any bit they're allowed?
I don't know.... there seem to be some odd correlations here.