Another good reason for indexing: When “market professionals” make a bet on a part of the market to outperform the rest, they’re often wrong. Here’s a Wall Street Journal article on why bond mutual funds let investors down. In short, “Most intermediate funds held far fewer of the safest bonds than were in the index.” And if you held a fund based on the index, you weren’t making a gamble on which bonds would do the best (an ill-fated gamble, it turned out). My favorite bond index fund: The Vanguard Total Bond Market Index fund.