The grand hilbert hotel is a metaphor about infinity. If a hotel has an infinite number of rooms, it will have enough room for him. If every room is full, they can all still move up by one room number. Infinity means you can always shift everyone up by 1 room number.

The ship of theseus is a philosophical question about whether it’s still the same ship after having every board and nail in it replaced over centuries of repairs gradually replacing all of its parts.

Asking if Sisyphus is happy is a reference to a famous Albert Camus (French absurdist philosopher) quote “One must imagine Sisyphus happy”