What does it mean to be in a den?

This sentence means to throw an egg at a stone, which is a metaphor for offending people and things beyond one's ability.

The down-to-earth legend originated in the Han Dynasty, and it became more and more complicated when it spread to later generations. No one should break the ground with his feet on the ground or the opposite posture. Anyone who violates this taboo will bring disaster and suffer bad luck. Later, it gradually evolved into an idiom to describe a person who committed a crime and caused himself a disaster.

It is a taboo for our people not to dig in the tiger's den. According to folklore, if you break ground in the direction of Tai Sui, you will find a kind of moving meat, which is the embodiment of Tai Sui. If people's fate is smooth, their luck is bad, and their life expectancy is reduced, they will suffer death. Therefore, people are most afraid of being too old, and they are often as scared as tigers. Those who are fierce and difficult to provoke are called "Tai Sui". Dare to break the ground on the lion's den has become the mantra of local ruffians and hooligans to scare people.

According to historical records, Tai Sui is a celestial body assumed by the ancients. It moves at the same speed as Jupiter, but in the opposite direction. In which area and direction Tai Sui arrives, there is a fleshy thing underground, which is the embodiment of Tai Sui. Breaking ground in this direction will disturb Tai Sui. This is the origin of "it will be a disaster to break ground on the lion's den"