Iconic Tour

Tony Robbins and Warren Buffett agree this is the biggest risk you can take with your money

Tony Robbins
David A. Grogan | CNBC

When it comes to investing for your future, Tony Robbins wants to warn you against a big mistake: trying to time the ups and downs of the market.

No one can predict the future, Robbins argues, and says legendary investors like billionaire Warren Buffett and hedge fund titan Ray Dalio agree.

"Your plan can't be based on trying to time the market because you're going to be wrong," Robbins tells CNBC's "Fast Money" Wednesday, speaking from the Iconic conference presented by Inc. and CNBC.

Tony Robbins: An evangelist for life change
Tony Robbins: An evangelist for life change

Instead of buying and selling as the market tides change, Robbins says to think long term.

"[Y]ou can't afford to try to time the market," he says. "What you have to do is study the long term elements, and you have to have a diversification plan that protects you when you're wrong."

Buffett has also been a prominent advocate for this type of "buy and hold," strategy — so much so that he made a bet that the S&P 500 stock index (a passive measure of the market as a whole) would outperform hedge funds (which actively change investments). Now, it looks like he's likely to win that bet, which will bring him an extra $2 million in prize money.

Robbins also points to advice from Ray Dalio, who founded the world's largest hedge fund, Bridgewater Associates. Even he has trouble spotting the right times to enter and exit investments.

"If Ray Dalio, with $160 billion in assets and a guy that has made money 23 out of the last 26 years says, 'I can't time the market,' no one is going to time the market perfectly."

So for Robbins, the best idea is to take the long view. And, both he and Buffett suggest considering investing in low cost index funds to do the job.

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