In the Northern Song Dynasty, there was a famous painter named Wen Tong, who was a master of bamboo painting at that time.

in order to paint bamboo well, Wen Tong keeps drilling around in the bamboo grove all the year round, whether it is spring, summer, autumn and winter, whether it is windy or rainy, or sunny or cloudy. In dog days, the sun's head is on fire, and the ground is hot. However, Wen Tong still ran to the side of the bamboo grove facing the sun, stood in the baking sunshine, and observed the changes of bamboo with rapt attention. He measured the length of bamboo knots with his fingers for a while, and then recorded how dense the bamboo leaves were. Sweat soaked his clothes and his face was sweating, but he didn't wipe it with his hands even once, as if nothing had happened.

once, a strong wind blew in the sky. Then, there was lightning and thunder, and a heavy rain was coming. People are running home. Just then, Wen Tong, sitting at home, grabbed a straw hat in a hurry, buckled it on his head and ran straight to the bamboo grove on the mountain. Hardly had he stepped out of the gate when the heavy rain began to splash water with a washbasin.

Wen Tong is bent on seeing the bamboo in the storm, but he can't afford the rain and the slippery road! He lifted his robe, climbed the hillside and ran to the bamboo forest. Panting, he ran into the bamboo forest, and without taking care of wiping the rain on his face, he watched the bamboo unblinkingly. I saw bamboo in the wind and rain, bending down and nodding, swaying. Wen Tong carefully kept in mind the posture of bamboo being beaten by wind and rain.

Due to Wen Tong's careful observation and research on bamboo for many years, what changes have taken place in the shape of bamboo in spring, summer, autumn and winter? What is the difference between the color and posture of bamboo on rainy and snowy days? What's the difference between bamboo under strong sunlight and bright moonlight? He knows exactly what different bamboos look like. So when you draw bamboo, you don't need to draw a sketch at all.

A man named Chao Buzhi praised Wen Tong and said, Wen Tong has already got a plan.

Later, "having a plan in mind" became an idiom, which was used to mean that people had already made up their minds to decide what to do before they did anything.