The three stories come together in a single thread in the last part of the story. All three has some part in their body; eye, liver and kidney, which is replaced. It has been donated by the other, but in truth which they all come to find is been stolen from some other’s body. And these three parts that is liver, eye and heart are stolen from one person. So the question, is these three persons are the one person from whom body parts are stolen? Or the one person is still the same person after his or her body parts are replaced? This is the paradox, I think, expressed through the title of the movie.
http://www.theindivisual.in/2013/07/reflection-on-movie-ship-of-theseus.html