Why Did Time Go Back Again?

The first thing Lin Yu does when he wakes up every day is to turn on his phone and look at the date to determine whether it is "tomorrow" or "yesterday". Unlike the rest of the world, his timeline seemed messed up. Time went back randomly and uncontrollably, and in one case, he even went back to 10 years ago. At first, he enjoyed it. It's like a game with infinite rewinds. In this game, he can do whatever he wants. The only problem is that he still doesn't understand whether this "retrospection" will end...