However, we have to deal with a design issue an not a fundamental principle. The books of a library have been carefully classified by type, subject and author. This classification makes it easier for people to find books. People would be lost without this classification. However, the books at home are simply put on a shelf without any order.
People classify everything they can.
The principle of inheritance is based on the principle of classification. Objects within a derived class will inherit from the original class. A classification is based upon common characteristics or similitudes and it is structured. This help us to find our way through a kind of complexity. It helps us to understand and to memorize.