John Bogle, founder of Vanguard and creator of the first index mutual fund, opens The Little Book of Common Sense Investing with his foundational, deceptively simple premise: broad-market index investing, holding the entire market at minimal cost rather than attempting to select superior individual stocks or fund managers, produces genuinely superior long-term returns for the overwhelming majority of investors.

Bogle's foundational argument:

• He argues that collectively, all investors as a group necessarily earn the market's aggregate return before costs, meaning the actual determinant of any individual investor's relative performance compared to this aggregate benchmark is largely a function of the costs — fees, trading expenses, taxes — incurred pursuing that return
• Since active management, attempting to select superior stocks or fund managers, inherently incurs higher costs than passive index investing, Bogle argues this cost differential alone virtually guarantees index investing's long-term performance advantage for the average investor, regardless of any individual active manager's stock-picking skill
• Bogle draws directly on his own decades of experience in the mutual fund industry, including his pioneering creation of the first publicly available index fund, lending his argument considerable practical grounding beyond pure theoretical argument

This foundational premise sets up the book's overall project: presenting extensive historical data and reasoning supporting index investing's superior long-term performance, while directly countering common objections and misconceptions about this approach.