Why can Lin Beixing go back to the past?

Because this is the setting in the TV series, as long as Lin Beixing deletes a short message from her old mobile phone, she can cross back to high school. But when Zhang Wansen falls from the lighthouse, she will come back to reality, just like having a dream, but it is very real.

Lin Beixing accidentally crossed into parallel time and space, and realized that the person who had not noticed before was Zhang Wansen. In the process of returning to the past and reality again and again, Lin Beixing also knows that the reason for his return is related to Zhang Wansen. When she returned to reality a few times ago, the last message she saw was that Zhang Wansen had fallen from the tower, so Lin Beixing had been protecting Zhang Wensen because she didn't want to return to the real world.

Plot introduction:

"Flash, flash, flash, flash, flash, flash, flash, flash, flash, flash, flash, flash, flash, flash, flash, flash, flash, flash.