Puzzle & Thinking Games · 57

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 design side has its own twist: Puzzle difficulty is not just solution length. A short solution can be hard if the key idea is hidden, while a long solution can feel easy once the pattern is clear. Nothing becomes more suspicious than a perfectly empty corner of a puzzle board.