Puzzle & Thinking Games · 6

Puzzle designers use symmetry as both help and misdirection; a repeated pattern can reveal structure or convince the player to assume two sides behave the same when they do not. Put that beside this bit of history: Sliding-block puzzles are difficult because open space is the real resource; every move spends and relocates the one gap that makes future moves possible. The phrase 'there must be a trick' is often correct and rarely comforting.