Why did Confucius use water to describe people?

The water flows endlessly and is the milk that nourishes all living things. It has virtues. Water does not have a certain shape, whether it is square or long, it must flow downward, it is gentle and gentle, and it has feelings and meaning. Water penetrates mountains and rocks and cuts through stone walls. It has no fear, it has ambition. Everything that enters the water will be able to wash away the dirt, and it is good at teaching... From this point of view, water is a true gentleman!

Confucius wanted his disciples to work hard to learn these beautiful qualities of water, and hoped that his disciples would become true gentlemen.