There are ordinarily only two players, since competition between more than two generally leads to temporary alliances to defeat whichever player acquires an early advantage, and strategy succumbs to politics. Contrary to some common assertions, there is an element of luck even in abstract strategy games. For instance, a player might make a move without seeing its value, and later find that any other move would have lost the game. But regardless of such considerations, playing an abstract strategy game is an exercise in logical thought. 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.