The History of Mahjong Solitaire
A single-player tile-matching game named after, and visually borrowing from, a completely different four-player game it has almost nothing else in common with.
Borrowed Tiles, New Game
Mahjong Solitaire (also called Shanghai) is not a traditional Chinese game - it's a Western invention from the early-to-mid 20th century that repurposes the beautifully illustrated tile set from the four-player game Mahjong (itself a 19th-century Chinese creation) for an entirely different, single-player matching puzzle with none of the original game's melds, discards, or scoring hands.
Exactly who first combined a pair-matching solitaire format with Mahjong tiles is genuinely unclear, with competing claims stretching back decades before the computer era - what's certain is that the pairing didn't become a global phenomenon until it made the jump to personal computers.
A 1980s Computer Screen Staple
The game reached a mass audience through early computer versions in the 1980s, most notably Activision's 1986 'Shanghai' for the Macintosh - popular enough that 'Shanghai' became, and in many places remains, an alternate name for the whole genre of solitaire tile-matching games built around the classic layered layout.
The layout that gives the game its name - a stepped, pyramid-like mound nicknamed 'the Turtle' - became so strongly associated with the genre that most implementations, including this one, default to some variation of it rather than inventing a new shape.
A Solvable-By-Construction Puzzle
Unlike a game such as Sudoku or a Nonogram, where a puzzle's solution is checked for uniqueness after being designed, a Mahjong Solitaire deal is normally guaranteed playable a different way: many implementations, including PaperGames's, build the deal by working backward from an empty board, replaying a legal removal sequence in reverse to decide which symbols go where.
That guarantees at least one winning path exists from the very first tile placed, but - exactly as with a real deck of Klondike solitaire cards - it says nothing about whether any particular sequence of matches a player actually makes will reach it, which is why getting stuck partway through a perfectly solvable deal is a normal, expected part of the game rather than a sign anything went wrong.