One day, a novice asked Ch'an Master Wu-ming, "Master, you have said that when we practice Buddhism we should make the great vow to save all beings. What if there is a person who is so evil that he can no longer be considered a person, should we save him?"
The Master did not respond immediately. In a short while, he took his pen and wrote the [Chinese] character 'me' upside down and asked, "What is this?"
"This is a character that has been written upside down."
"What character is it?" inquired the Master.
The novice answered, "It is 'me'."
"Can an upside down 'me' be considered a character?"
The novice replied, "No."
"If it is not a character, then why did you say that it is 'me'?"
Upon hearing this, the novice changed his mind and said, "Yes, it can be considered a character."
The Master challenged his response, "If you say that it is a character, then why did you say that is is upside down?"
The novice did not know how to respond to this question.
"A properly written character is a character, and an upside down character is a character," continued the Master. "You said that the character is 'me' and recognized that it is written upside down because you knew the correctly written 'me'. On the other hand, if you did not know the character, and if I have written it upside down, you could not tell difference. If someone told you that the upside down 'me' is the character 'me', the next time when you see a correctly written 'me', you would think that it was upside down."
The Master further explained, "Similarly, there is no difference between a good and an evil person. Regardless whether a person is good or evil, you should help the person to bring out his or her true nature. If one is clear about one's true nature, then one's behaviour would not be difficult to correct."
(Source: Hsing Yun's Ch'an Talk, Book 2)