Knowing when enough is enough just could be the secret to investing success

John "Jack" Bogle, who died in January at age 89, founded the mutual fund giant Vanguard in 1974. A year later he made market history by creating the first Standard & Poor's 500 equity index fund for regular individual investors. The low-cost broad-based index investing movement he pioneered revolutionized investing for ordinary savers.

Barron's recently published a 2007 essay by Bogle that had been commissioned but unpublished. The column emphasizes four main points: Individuals should focus on keeping costs down, broadly diversify, allocate their assets prudently and stay the course.

Bogle also recommended a simple portfolio strategy consisting of a bond index fund and a stock index fund, adjusted for the investor's age. Barron's did the numbers. A 40-year-old investor who followed Bogle's advice would have earned an annualized return 7.3%. That would turn $100,000 into $236,000 by May 1, 2019.

His advice sent me looking for an interview I had with Bogle following the global credit crisis and the plunge in the stock market about a decade ago. He followed his own advice.

"I am a believer in diversification. You buy index funds for stocks, and your bond portion should equal your age," he said. "This is how I invest, so I know how little it's hurt me to have a substantial position in U.S. bonds."

I also think Bogle's low-fee keep-it-simple approach encourages people to spend more time on what really matters to them. He called it knowing when "enough is enough." He wonderfully captured the idea of "enough" in a commencement address at the Georgetown University business school in 2007 — the same year as his unpublished article. His talk closed with a poem by author Kurt Vonnegut.

"True story, Word of Honor":

now dead,

and I were at a party given by a billionaire

on Shelter Island.

I said, "Joe, how does it make you feel

to know that our host only yesterday

than your novel 'Catch-22'

has earned in its entire history?"

And Joe said, "I've got something he can never have."

And I said, "What on earth could that be, Joe?"

And Joe said, "The knowledge that I've got enough."

Those are words to invest and live by.