Damn I wish I could reference the author of this quote…
Gamesmastering is something like trying to write & direct a screenplay while the cameras are rolling, for half a dozen prima donnas who are all demanding they’re the star of the movie, and you’ve also got to do the special effects and play *all* the bit parts yourself.
Under An Outlaw Moon 
My rampaging ego compels me to reply to a six-year-old post. I think I wrote that in an essay on GMing Legend of the Five Rings. (http://chrysanthemumroad.tripod.com/writing/TaoGM.htm)