A final word to the Dungeon Master from the authors. These rules are intended as guidelines. No two Dungeon Masters run their dungeons quite the same way, as anyone who has learned the game with one group and then transferred to another can easily attest. You are sure to encounter situations not covered by these rules. Improvise. Agree on a probability that an event will occur and convert it into a die roll – roll the number and see what happens! The game is intended to be fun and the rules modified if the players desire. Do not hesitate to invent, create and experiment with new ideas. Imagination is the key to a good game. Enjoy!
--J. Eric Holmes, Basic Dungeons & Dragons (1977)