In reading this book, DMs and players should remember that situations will arise that are not covered in the rules. In these situations, the DM should use personal judgment to resolve any problems. The freedom allowed to players and DMs is one of the strengths of the D&D rules system, and that has been continued here.--Dungeons & Dragons Fantasy Adventure Game Expert Rulebook, edited by David Cook with Steve Marsh, page X4 (TSR, 1981). Emphasis mine.
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