Each font consists of strokes. In order to reflect the three-dimensional sense, we should first write the strokes into a hollow closed shape (mostly rectangular). Simple horizontal and vertical strokes are best written, and crossed strokes should also be written in closed shapes (lines cannot cross). This step can be omitted after proficiency (brain supplement is enough).

Then imagine that the light is projected from the upper left corner, and all the lines (blue parts) that can be illuminated by the light are removed. Obviously, the upper horizontal line and the left vertical line must be deleted.

The intersection of strokes is the key, so we must first imagine the hollow intersection of solids (you can draw it first, and then you can write it directly after you are proficient), so when you meet the intersection, disconnect the lines first. Each stroke of solids is composed of closed shapes, and these shapes are composed of lines.

So the formation process of three-dimensional characters is:

Lines → (composition) → strokes with closed shapes → (composition) → light irradiation → (removing some lines) → three-dimensional characters.

Simply put, lines form three-dimensional characters under the irradiation of light.