A more thorough explanation:

Definition: Is qui omnino desipit (is kwI om-nI-noh dee-sip-it) is a Latin phrase that refers to a person who is completely void of reason. It was historically used to describe an insane person, not an idiot.

Example 1: John was found wandering the streets, talking to himself and behaving erratically. His family took him to a mental health facility where he was diagnosed with schizophrenia. He was described as is qui omnino desipit.

Example 2: The king's advisor warned him against making a certain decision, but the king ignored the advice and suffered the consequences. The advisor remarked that the king was acting like is qui omnino desipit.

These examples illustrate how the phrase is used to describe someone who is completely lacking in reason or sanity. In the first example, John's behavior is so irrational that he is considered insane. In the second example, the king's decision-making is so foolish that he is compared to someone who is completely void of reason.