A good abstract game can therefore be thought of as a family of potentially interesting logic puzzles, and the play consists of each player posing such a puzzle to the other. Good players are the ones who find the most difficult puzzles to present to their opponents. The design of a good abstract game must therefore allow an inexhaustible supply of interesting puzzles to be discovered in the possible positions of its board. Equally important, these puzzles must be discoverable and to some degree solvable by the players. Anthropologists from another planet who wanted to study the way human beings think would do well to study our abstract strategy games.
Depth means that human beings are capable of playing at many different levels of expertise.
For most board positions, until the last stages of the endgame, the puzzle of finding the best move should not be completely solvable. In a deep game, a player must exercise nice judgment in deciding what is the best move in most situations. Depth gives a game lasting interest because the player continues to learn how to improve his play for a long time. But in addition to depth a good game must have clarity . Clarity means that an ordinary human being, without devoting his career to it, can form a judgment about what is the best move in a given situation.