I've long been a very strong proponent of indexing. I've posted heavily on the topic here in this blog, but a quick recap of why indexing is so brilliant is probably in order.
In any given year (ignoring costs), about 50% of all active equity managers will beat the market, while 50% or so will trail the market. This has to be the case. It cannot be the case that the majority of equity managers beat the market, because the market is largely actively managed. Simply put - there has to be winners and losers.
In reality however, more than 50% of active managers trail the market because of trading costs and fees. These costs can easily be 1-3% or more per year, enough to cause a significant drag on performance. Bogle realized that if you just bought "the market" and didn't trade and didn't spend money on active management, you could reduce the total costs to a nearly trivial amount, less that 1/10 of a percent. The simple outcome of this strategy is that the "indexed" fund will beat more than 50% of all active funds in a given year, and in the long run will beat most active funds.
You might be thinking, surely 1 or 2 percent isn't that much? Well, consider an investor with a million dollars: 1% is $10,000 per year every year. This is a significant performance drag.
Or consider if you take $1,000 and compound for 40 years at 8% you'll end up with about $21,724. But if you compound only at 7%, just 1% less per year, your original $1,000 will only grow to $14,974. The 8% investment is worth 45% more than the 7% investment.
This is why, in the long run, indexing always wins. It's why I personally am 97% indexed and why I strongly advocate it for all investors (including pension funds).
And this is Bogle's legacy. He's enabled many ordinary investors to be much wealthier than they would have bee had they stuck with active managers.
As Mark Hulbert says:
"... he bet his entire career and his mutual-fund firm on the notion that the vast majority of active fund managers would be unable to beat a simple index fund. And there was hardly a single calendar year since 1976, when he created the Vanguard 500 Index Fund in which he was wrong."