Passage Summary: Just because a pill helps a normal person sleep a bit doesn't mean it's a cure for a medical sleep disorder, especially since it didn't even work that well on the healthy people.

Conclusion: The ability of melatonin to induce sleep does not necessarily mean it is an effective treatment for insomnia.

Reasoning: Most studies on melatonin used subjects who did not have insomnia, and even in those studies, only a small portion of participants showed significant effects.

Analysis: The argument highlights a gap between 'inducing sleep' in healthy people and 'treating insomnia' in patients. To strengthen this, we want to further decouple these two concepts. If we find out that the underlying causes of insomnia are unrelated to the mechanisms melatonin affects, or that insomniacs are specifically resistant to it, the argument becomes much stronger. Look for an answer that suggests the results seen in healthy subjects are not applicable or transferable to those suffering from clinical insomnia.