What does John 8:5 mean?

Leviticus 20:10 and Deuteronomy 22:22 prescribed the death penalty for couples who committed adultery. However, the Pharisees who have brought this woman have only accused half of the guilty parties: the woman. This raises a serious problem with their attack on Jesus. Their goal, as shown in the next verse, is to trick Jesus into making one of two mistakes. As they see it, Jesus can either stone the woman, ruining His reputation for mercy (Matthew 11:19; Luke 6:36), and putting Himself at legal risk (John 18:31), or He can refuse and defy the law of Moses (John 8:6). In trying to show their superiority, however, these men have failed to fully follow the law themselves: they have not brought the guilty man!

Some interpreters believe this very fact plays into Jesus' response. The next verse indicates that Jesus writes something on the ground, silently absorbing questions until He chooses to respond. It's possible He was writing the very laws these men claimed to be following, in order to highlight their hypocrisy. Perhaps He wrote the names of the accusing Pharisees and their own sins. What, exactly, He was writing, we don't know. What we do know is that Jesus successfully answers this dilemma using a principle from which all Christians can learn. This is the difference between what we can do, and what we ought to do.