笔记本

Why does 笔记本 look like this?

This is a compound word: 笔 (bǐ) means 'pen/writing tool' (bamboo on top, brush hair on bottom), 记 (jì) means 'to record' (speech radical on the left, self on the right), and 本 (běn) means 'root/volume' (a tree with a line marking the base). Together, they form a 'writing record volume'—a notebook!