Why did the last 800 meters die in the illegal immigrant movie?

Physical overdraft. According to the Douban film, bilal swam for dozens of kilometers, but it was still 800 meters away from the finish line, so he was exhausted. He drowned when he swam for the second time. Synopsis: Simon is a swimming coach in the swimming pool. He was attracted by bilal's seriousness, and gradually became fond of the young man. Simon tried to dissuade bilal from learning to swim in order to cross the Lamanche Strait, but when he learned that bilal had gone to England to meet his girlfriend Mina, Simon, who was going through the divorce procedure, decided to help him.