Because cats are like tigers and dogs are like wolves. Tigers belong to the feline family, and are similar to cats in appearance; dogs began as wolves in East Asia, but there is a big difference between wolves and dogs in terms of temperament. The meaning of "like a wolf like a tiger" is as fierce as wolves and tigers.

Singularities are stereotyped words in the Chinese vocabulary. The idioms, which are said by all people, become in the language, so they become idioms. Most of the idioms are four words, but there are also three words, five words and even more than seven words. Chengyu is a major feature of traditional Chinese culture, which has a fixed structural form and a fixed way of saying things, and expresses a certain meaning.