Passage Summary: You can't effectively trick yourself into believing a lie to break a habit, so you need a doctor or someone else to provide the exaggerated warning.

Conclusion: People cannot easily use 'exaggeration' strategies to break habits unless a third party provides the warning.

Reasoning: These strategies rely on deception, and because you cannot easily deceive yourself, you need someone else to do the lying for you.

Analysis: The argument relies on a critical 'Gap' between the necessity of deception and the source of that deception. It assumes that a person is incapable of successfully deceiving themselves in the way a doctor could. If it were possible to effectively lie to yourself about the dangers of a habit, the requirement for a 'third party' would vanish. Therefore, look for a Necessary Assumption that confirms the difficulty or impossibility of self-deception in this specific context. The argument 'needs' it to be true that you can't be both the deceiver and the deceived simultaneously.