"Flowers in the wall and fragrance outside the wall" means that the flowers planted in the wall are unremarkable and unpopular inside the high wall, but the fragrance spreads outside the wall, giving people a beautiful feeling and infinite yearning. Metaphor means that people have made achievements, but they don't know it internally, but outsiders know it first. Metaphorical achievements are not valued by this department, but appreciated by other departments.

It's from "Die of Youth" by Hai Yan: "There are flowers in the wall and incense outside the wall. It's all like this. If you don't do it, forget it."