What is the meaning of smoothing willow in calligraphy?

I am a calligraphy lover, but my knowledge is too shallow to answer, so I have the right to communicate. The word "plain" should be understood as writing paper, which is open and flat. There are two understandings of willow thinning. 1, willow in cold weather, with sparse branches and leaves, is more flexible and beautiful. Persevere and never bend around. It is interdependent with the characteristics of toughness, beauty, curvature, firmness and roundness (middle) emphasized by calligraphy art. 2. yehliu, with proper density, natural arrangement and patchwork. The layout of metaphor is wonderful and natural. Foolish and foolish, if there is anything wrong, please accept it.