Zhang Wansen jumped off the lighthouse because he loved Lin Beixing deeply, but this love could not be answered for various reasons. On the lighthouse, he saw the scene of Lin Beixing's intimacy with the protagonist. He felt extremely painful and finally chose to jump into the sea.
Zhang Wansen has been silently guarding Lin Beixing and even gave up his life for her. However, fate always played tricks on him, making him miss Lin Beixing again and again. On the lighthouse, he saw the future of Lin Beixing and the protagonist, knowing that he could not spend the rest of his life with her, and his heart was full of despair.
He went through a fierce struggle in his heart and finally chose to jump into the sea. This jump is not only the despair of one's own love, but also the helplessness and struggle of fate. His death became an opportunity for Lin Beixing to travel through time and space, and also made her realize the existence of Zhang Wansen.
With the efforts of Lin Beixing, she finally discovered Zhang Wansen's sincerity. She regretted not cherishing this feeling and decided to make up for Zhang Wansen's regret as much as possible in the process of traveling through time and space.
Zhang Wansen jumped into the sea not only because of his despair of love, but also because of his resistance to unfair fate. His death made Lin Beixing realize the true meaning of love, and also made the audience feel the impermanence and helplessness of fate. In this process, Zhang Wansen's persistence and sacrifice became the driving force of Lin Beixing's progress and became an eternal memory in the hearts of the audience.