The game is the thing, and certain rules can be distorted or disregarded altogether in favor of play...
Know the game systems, and you will know how and when to take upon
yourself the ultimate power. To become the final arbiter, rather than the
interpreter of the rules, can be a difficult and demanding task, and it cannot
be undertaken lightly, for your players expect to play this gome, not
one made up on the spot. By the same token, they are playing the game
the way you, their DM, imagines and creates it. Remembering that the
game is greater than its parts, and knowing all of the parts, you will have
overcome the greater part of the challenge of being a referee. Being a
true DM requires cleverness and imagination which no set of rules books
can bestow.