1. Never practiced. Hand-painting needs constant practice, and only constant practice can improve your hand-painting level.
2. Did not master the basic skills. Hand-drawing needs to master some basic skills, such as lines, shadows, perspective and so on. If these skills are not mastered, line drawing will be scribbled.
3. I didn't pay attention to the details. When hand-drawing, you need to pay attention to many details, such as the thickness, length and direction of lines. If we don't pay attention to these details, the line drawing will be scribbled.
4. Don't grasp the proportional relationship. When hand-drawing, we need to pay attention to the proportional relationship between the parts of the product. If you don't master these proportional relationships well, it will lead to scribbling.