Cathy had tried swimming many times since she had grown up. However, no matter how hard she tried, she was never able to go underwater for more than a few seconds. It was very annoying, as going underwater was supposed to be part of the test she was helping her friend with, for the lifeguard course.
But her friend kept encouraging her, saying that he needed to practice rescuing, giving her mouth to mouth, and a chest massage. She wanted him to get certified, so she helped him, every day. Even though he already knew the process for mouth to mouth and massage, he still insisted on practicing with her every day, explaining that he has to pass the whole test, not just part of it. So he has to practice all of it each time.