New Delhi, Aug. 15 -- It usually starts with a phone call.

For Ajay Lakhotia, it was his father's. Buy railway stocks, he said. They'll become 3x in a year. The tip had travelled from a friend on a morning walk, through a father, to a son who had spent two decades in investment banking and venture capital. And here is the part Lakhotia admits with a laugh: he bought them too.

"Take a step back and understand the phenomenon of investing," he says. "You realise it is perhaps the largest consensus-based social commerce activity in India." A nation of 1.4 billion people making its most consequential investment decisions the way it picks a wedding caterer - on hearsay.

That call, repeated in crores of Indian homes every day, became the prob...