| A rule in a game must be easily understandable and unambiguous. It must be completely clear: no interpretation must be needed by the GM or players to make the game playable. It must not encourage misinterpretation. |
| All rules must work properly. The more rules you put into a game, the greater the chance that there will be some rules that don't work properly, and that a number of rules will interact in an unforeseen way to produce an undesirable effect. |