Why do so many children in India receive antibiotics for diarrhea when guidelines call for oral rehydration salts instead? A new study, co-authored by Manoj Mohanan, finds that the main culprit is not a lack of knowledge, financial incentives, or shortages of recommended treatments. Rather, it is a persistent “know-do gap”: providers know the guidelines but prescribe differently because they mistakenly believe parents expect antibiotics. In a sample of more than 2,200 providers across 253 towns, 70 percent prescribed antibiotics even without signs of bacterial infection, and among those who knew antibiotics were inappropriate, 62 percent still prescribed them. Randomized experiments showed that when patients expressed a clear preference for oral rehydration salts, antibiotic use dropped by 17 percentage points, especially in pharmacies. The findings highlight how communication and perception — not profit motives — drive misuse. Mohanan notes that empowering caregivers to voice preferences or running public campaigns to correct misperceptions could significantly curb inappropriate prescribing and strengthen global efforts to fight antibiotic resistance.