A man goes to work at the same time each day and travels part of his journey facing forwards and the remainder facing backwards. When he returns at the end of his working day, he only faces forwards.
How can this be?
He works in the engine room of a liner! To get to work, he walks along the decks from his cabin facing forwards, and down the ladders between decks facing backwards. However, when he finishes, he only needs to face forwards to climb the ladders again and walk along the deck back to his cabin.