Arne Slot's seamless succession to Jurgen Klopp as Liverpool manager has shown he is not only an outstanding coach but a fast learner - but he was given a harsh lesson in one of the game's oldest rules on a wild afternoon in Devon.
Never play fast and loose with the grand old FA Cup.
The sight of Plymouth Argyle, bottom of the Championship, embarrassing Premier League leaders and the previously all-conquering Liverpool with this fourth-round victory was a compelling response to those who would to attempt to downgrade the magic and history of the competition.