The idiom of "Fish in Fish Soup" originated from an allusion in the Tang Dynasty. An official invited his friends over for dinner, and to show off his wealth, he decided to cook a fish soup. However, when it was time to eat, he picked out the fish and left a pot of clear soup. His friends were very angry because this was a waste of ingredients and did not reflect the host's culinary skills. Later this practice became an idiom describing behavior that is vain and of no real value.

"Fish in the soup" can also be used to describe a person who hides his true intentions and doesn't let people see what he really thinks. For example, in a business negotiation, a person may falsely claim that he is only negotiating on behalf of his company, but in reality he may have other connections and interests, and this is 'the fish in the fish soup'. This idiom reminds people to be wary of things that appear to be no problem on the surface, as real risks may be hidden.

In daily life, 'fish in the fish soup' can also be used to describe a situation where the appearance and substance of a thing are not the same. For example, if a product has a very well-written tagline, but the actual use of the product is very poor, this is a 'fish in the soup'. In this case, people need to examine the inner essence of things to understand their real value and effect, and not be confused by the superficial fancy.