One day in the year 489 B.C., Confucius led his disciples to the State of Cai via the State of Chen. When they passed by the State of Chen, they were surrounded by the people of Chen.
For seven days and nights in succession, they hadn't eaten one grain of rice. They were so hungry that they couldn't get up from bed.
Later, after much effort, one of his disciples Yan Hui somehow obtained some rice. The rice was washed and cooked, and when it was almost done, Yan Hui suddenly stretched out his hand to grab a handful of rice from the steamer, put it into his mouth and swallowed it.
Confucius, lying at a distance, saw all this by chance, but pretended that he had seen nothing and didn't say a word.
After a while the rice was done. Yan Hui respectfully came to Confucius and asked him to take his meal.
Confucius slowly sat up in his bed and said to Yan Hui:
"A short while ago I had a dream. I dreamed of my deceased father. If the rice is clean, I would like to make a sacrificial offer to him."
Yan Hui replied hurriedly:
"Master, the rice is not clean, and it's unfit for sacrifice."
He then continued:
"Some soot has just fallen into the steamer and soiled the rice. It is a pity to throw the rice away, so I picked out the sooted rice and ate it."
Confucius suddenly saw the light. He sighed and said:
"It goes without saying that one can trust one's own eyes. But now it seems that one's eyes cannot be trusted entirely. It goes without saying that one can trust one's own mind, but now it seems that one's own mind cannot be trusted entirely either. Disciples, keep this in mind: It is not easy to thoroughly understand a person after all."