Despite appearances, puzzling is not a solitary game: every move the puzzler makes, the puzzlemaker has made before; every piece the puzzler picks up, and picks up again, and studies and strokes, every combination he tries, and tries a second time, every blunder and every insight, each hope and each discouragement have all been designed, calculated, and decided by the other.

Life: A User's Manual (1978). Preamble