During the Warring States period, the philosopher Yang Zhu was known for his extreme self-interest
Once, Yang Zhu visited his friend Ji Liang, who happened to be unwell and lying in bed. Ji Liang's son, upon seeing Yang Zhu, said tearfully, "Uncle Yang, my father's illness looks quite serious. Could you help me fetch a doctor to examine him?"
Yang Zhu took a look and comforted Ji Liang's son, saying, "Nephew, don't worry. In my view, your father's illness is not serious. With proper care, he will recover soon."
But Ji Liang's son refused to listen and immediately summoned three physicians.
The first doctor was named Jiao. Dr. Jiao examined Ji Liang and said:
"Your illness is caused by irregular temperature changes, imbalance of deficiency and excess, disharmony of yin and yang, and uneven hunger and fullness. Just take a few doses of medicine and you'll be cured—no need to worry." Ji Liang shook his head and said, "You're just an ordinary doctor. Leave!"
The second doctor was surnamed Yu. Doctor Yu took Ji Liang's pulse and said:
“Your illness is due to congenital deficiency, not something that formed overnight. It would be difficult to cure you with medicine.” Ji Liang, upon hearing this, praised, “You are a fine physician, skilled in your craft!”
The third doctor was surnamed Lu. Doctor Lu merely glanced at Ji Liang's complexion and said,
"Physiologically, you have no illness. Your condition is caused by mental factors, so no medication is needed. As long as you cultivate your mind and character, you will recover quickly." Ji Liang listened and praised, "You are truly a divine physician!"
He then sent the physician Lu away with many gifts. In truth, Ji Liang's illness had indeed stemmed from mental depression, and not long after, through emotional regulation, his condition fully recovered.
Later, the idiom "One Morning, One Evening" came to describe a very short period of time.
Source: *Liezi*, Chapter "Force and Destiny"
Meaning of the Idiom: Later, the Chinese idiom "一朝一夕" came to describe a very short period of time.