Bottom line thinking is the embodiment of the doctrine of the mean. Everything is the unity of quality and quantity, and its unity is in the category of "degree". From the perspective of materialist dialectics, the bottom line is a critical value from quantitative change to qualitative change. Once the quantitative change breaks through the bottom line and reaches the joint point of qualitative change, the nature of things will change fundamentally. The biggest unity of opposites in bottom line thinking is the organic combination of two joint points, namely "bottom" and "top". If you don't keep the bottom, it is difficult to reach its "top". If you don't climb high, you don't have to keep the bottom. This is called "keeping low and keeping high".