Physics problem, about hardness. Why do most people write with HB pencils instead of plain paper?

Different hardness, HB soft, black, 4H hard, light color. Simply put, H stands for hardness and B stands for softness. Generally speaking, the so-called softness refers to the color depth of the traces drawn by the pencil on the paper. The harder the lead of a pencil, the lighter the color, and the sharpened refill is not easy to smooth. The greater the number in front of the hardness unit h, the harder it is, such as h, 2H, 3H, etc. Here 3H is the lightest color, which is suitable for drawing thin lines, but the paper is also easy to be damaged. Soft is the opposite. The softer the lead, the darker the color, which is suitable for drawing thick lines, but the pen tip is easy to be smooth. For example, the pencils of B, 2B, 3B, ... HB are moderate in hardness and are suitable for daily writing and other purposes. 2B pencil is commonly used in drawing, and H is widely used in drawing, but there are also B, mainly according to needs.