Going Through the Back Door

Am currently reading a book about Chinese folk verses (民谣), and it contained an explanation about how the Chinese expression "走后门" (or "going through the back door") came about.

But first, the folk verse in question:

"看到别人走后门，别生气，
自己没有后门，别丧气，
一旦有了后门， 别客气。"

(民谣下的中国 - 当代顺口溜赏析，聂仁 著， 时代文艺出版社，2001）

("When you see others going by the back door, don't be mad,
When you don't have a back door, don't be discouraged,
When you finally have a back door, don't stand on ceremony.")

The English translation, unfortunately, do not rhyme like its Chinese equivalent.

The expression "走后门" apparently came about during the Northern Sung dynasty during the tenure of prime minister (宰相) Cai Jing (蔡京), who was known for being evil and corrupted, and for persecuting officials loyal to the previous emperor.

Cai was one day informed that a rich landlord had sent a thousand teals of silver "for favors rendered", and the goodies were waiting to be delivered to Cai.

But the problem was, the silver in question were manufactured during the reign of the previous emperor. So what should be done?

Well, fret not. Cai thought for a moment and declared that the silver "should not enter through the main door, but through the back door."