Two timelines run at the same time. In the third episode, when the female lead gets on the bus, the second timeline begins. In the first line the story continues with her in the small town, continuing her interaction with her childhood sweetheart: Yu Jian. In the second timeline, it's Xia Guo who didn't give up on going to Shanghai and now she will have another story with another man in her life, her boss: Xue Yu Ming.
The two male protagonists (Yu Jian and Xue Ming) have completely different profiles. But, the one who has the most screen time is Yu Jian (Liu Xue Yi) who crosses both timelines, and will have to make choices in both timelines.
What will be most extraordinary about Xia Guo's choice that we will know at the end of the drama? The choice she makes in each timeline is to get to know that something more extraordinary, less ordinary in life.
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Observation:

I think the third boyfriend in the story won't be as important in the plot. The two men in her life: Yu Jian and boss Xue Yu Ming. (but there are two stories happening at the same time).The First Xia Guo chooses to stay in the small city and continue her love story with Yu Jian. The other Xia Guo gets on the bus and chooses to go to the big city and gets a great job. And at a certain point she gives up on Yu Jian completely and starts a love story with boss Xue Yu Ming.
What I want to say is: some say that the male lead is Xue Yu Ming. But in reality it's as if there were two male leads (who win the heroine) each in a different timeline. These male leads (Yu Jian and Xue Yiu Ming) are completely different, they are like water and wine. So: whoever prefers the charming boss, says that the male lead is Xue Yu Ming. Those who prefer the naive, honest and loyal male lead, attached to their family and their dreams of starting a family and never giving up on taking care of their parents, those who prefer this profile more (will say: Yu Jian is the male lead).
However: what happens is that the one who has the most screen time is Yu Jian. He crosses both timelines, he will have in both timelines also make diametrically opposite choices.
But in practice: There are two dramas in one drama, with their respective heroes. But they are two distinct genres of drama (forming a single TV show).