What does it mean to find a congratulatory letter when it rains?

He Han is the hero in the TV series My First Half Life. He once drove a hundred miles to give an umbrella to the heroine in rainy days. Therefore, some drama fans will remember the plot of He Han sending an umbrella in the rain.

Introduction of He Han's My First Half Life

He Han, played by actor Jin Dong, is an elite in the consulting industry. He is famous for his qualifications, professionalism and talent in the business world. He is a typical rational urban personality, and he is at ease in the face of business wars in the workplace. In the face of feelings, he and Tang Jing refused to talk about marriage after falling in love for ten years, and still put their career first in life. When they were involved in the same business war, "friendship is friendship, business is business" is still the principle he abides by.