Passage Summary: The author claims that while people should usually practice what they preach, logicians should be exempt from being logical, similar to how a doctor can be unhealthy but still provide medical care.

Conclusion: It is not necessary for logicians to be logical when they are discussing the subject of logic.

Reasoning: The author argues that just as a doctor doesn't need to live a healthy life to treat a patient, a logician doesn't need to be logical to discuss logic.

Analysis: The argument relies on a weak analogy between physical health and logical consistency. While a doctor's personal diet doesn't necessarily prevent them from prescribing the right medicine, a logician's failure to be logical during a discussion of logic would fundamentally undermine the very activity they are engaging in. The author ignores that being logical is a functional requirement for a discussion on logic, whereas being healthy is not a functional requirement for medical knowledge. It's a bit like a swimming instructor claiming they don't need to know how to stay afloat while teaching a class.