(an essential chess player tool)
"A cardinal rule for the best use of rooks in endgames: Use the rook to cut off the King." - Purdy
Drive the king to "death row" (anywhere along the edge of the board).
You do not need your king for this checkmate.
You must be able to do this checkmate effortlessly to call yourself a "chess player."
Openings teach you openings. Endgames teach you chess.