Today, Vanguard is synonymous with low-cost index investing. But as the firm marks 50 years since the launch of the first index fund, something surprising has happened: After decades of relentless gains, Vanguard’s share of the fund industry has plateaued. For most companies, that would be bad news. Yet Jack Bogle might have seen it differently. More than 30 years ago, Vanguard’s founder said he’d know his mission was succeeding when competitors became so cheap that Vanguard itself began losing market share.

On this episode of Trillions, Eric Balchunas and Joel Weber — joined by Bloomberg News cross-asset reporter Isabelle Lee — revisit Bogle’s legacy. They trace the unlikely rise of the index fund, why it took decades to catch on and how Vanguard’s low-cost model eventually forced the rest of Wall Street to change. They also explore what Vanguard’s plateau means now that the Bogle Effect has become so much bigger than Vanguard itself.