During his travels among the states, Confucius and his disciples were once besieged in the region of Chen and Cai, going without food for seven days.
Yan Hui managed to obtain some rice and promptly began cooking it.
As the rice was nearly done, Confucius observed Yan Hui snatching a handful from the pot and putting it into his mouth.
When the meal was ready, Yan Hui presented it to Confucius. Pretending he had not seen the act, Confucius said he wished to offer the rice as a sacrifice to his ancestors.
Hearing this, Yan Hui hastily explained, "That would not be proper. Just now, some ashes fell into the pot and smeared the rice. I removed the soiled portion and ate it myself."
Upon hearing this, Confucius sighed and reflected to his disciples, "People are inclined to trust their eyes, yet what the eyes see is not always the truth. People also tend to rely on their own judgments, but judgments can be mistaken. Remember, truly understanding a person is most difficult."