In our daily life, we often use the word "毛病 (máo bìng)" in Chinese. We can say "挑毛病 (tiāo máo bìng)" to describe someone who likes picking at others. When something goes wrong, we say "出毛病 (chū máo bìng)". The chronic diseases or bad hobbies or habits are called "老毛病 (lǎo máo bìng)". But why is a flaw or fault called "毛病 (máo bìng)"?
In ancient times, horses were used for dragging, loading, war and riding. Therefore, people at that time chose a horse strictly by judging from the color and shape of the hair. The word "毛病 (máo bìng)" originally referred to the flaws on the hair color of a horse, and a horse with flawed hair was of little worth.
Later, as the demand for horses decreases, the word "毛病 (máo bìng)" is seldom used by people, and it's no longer confined to choosing a horse. It has become a word meaning a person's shortcoming or fault.