Lee WA farmer, a small boat and three passengers who can’t be left alone together, set as a puzzle twelve hundred years ago.
A farmer has to get a wolf, a goat and a cabbage across a river. His boat holds him and one of them at a time. Left alone together, the wolf will eat the goat, and the goat will eat the cabbage. What is the fewest crossings it takes to get all three over safely?
Nobody said the boat has to come back empty.
Take the goat over and row back alone. Take the wolf over and bring the goat back with you. Leave the goat, take the cabbage over to the wolf and row back alone. Then fetch the goat.
The move people miss is the goat going back. Nothing forbids it, it just feels like losing ground.
Source: Attributed to Alcuin of York, Propositiones ad Acuendos Juvenes, Proposition 18, c. 800