A major shortcoming that should be avoided when drawing with a pen. Your school: The edges and corners of your school are still very sharp. In Song Dynasty, Guo's "Pictures and Experience, On the Gains and Losses of Using a Pen" said ... Engraving workers are suspicious of the pen, and their hearts and hands are hostile. When sketching, he was born with false horns. "In the Qing Dynasty, Tang Dai's" Sketch, brushwork "said:" The method of using a pen cares about the wrist, being gentle, being able to accept and release, not for a pen. The pen must use the center, and the statement of the center does not mean that the pen is correct. If you can use the sharp edge of the pen tip, the pen is round but not flat, otherwise it will be clumsy to use the pen root, or engrave or slant, and use a flat pen to take power. "