India, Aug. 30 -- A friend recently shared a story that captures India's payments paradox better than any statistic. His household help handed him Rs.500 in cash and asked that it be sent by UPI to his family in another state. He didn't know how to do it himself. But he knew UPI would deliver the money instantly, without fees. This small moment shows how India really works today: cash in hand, digital in transit. One rail begins the journey, the other completes it.

Which is why a viral tweet last week, struck a strong note. It argued, "Every rupee increase in UPI transactions reduces debit card usage by 14 paisa." The thread cited a State Bank of India (SBI) research report to triumphantly declare that UPI had overtaken cash in India. Th...