The Ship of Theseus, also known as Theseus's Paradox:
Before each voyage, the ship was repaired by replacing some of the planks, and over time all the planks were replaced, giving rise to an argument: does the ship remain the same or is it brand new? In addition, the question arises: if all the replaced planks were kept and another ship was built from them, which of these two ships would be the real one?