Every one has two halves. Study walks the annotated technique and records nothing; Drill makes you play it out against Stockfish, which will not cooperate with a half-learnt plan. Every position here was replayed and put to an engine before it was published, rather than remembered from a book.
Force the mate with no pawns on the board. Nothing here is negotiable.
Two rooks mate without any help from the king: one cuts off a rank, the other drives the king onto the next one. This is the pattern every other rook mate is built from.
King and pawn decides more games than any other ending, and it is pure calculation — one tempo either way is the whole result.
The most common endgame there is. Two positions from the fifteenth and eighteenth centuries still cover most of it.
A queen beats almost anything — except when stalemate gets in the way.
Which bishop you have, and which corner the king reaches, is often the entire game.
Compositions that taught everyone something no rule of thumb covers.