Vanguard’s index fund marked its 50th anniversary, reviving discussion around what drove its long-term impact on investing. The source argues that low costs, rather than indexing alone, were the key factor behind the fund’s success and broader adoption. The post also attributes Vanguard’s low-fee model to its mutual ownership structure, arguing that a high-cost index fund would have offered far less value. It further suggests Vanguard could have become a much larger mutual fund company even as an active-only manager because its low-fee structure would have remained a competitive advantage.