"I think [bitcoin] is very iffy," Robbins tells CNBC's " Fast Money " Wednesday, speaking from the Iconic conference presented by Inc. and CNBC. "I don't have a clue. I look at that as it's like going to Vegas."

Watching the price of digital currency bitcoin is a roller coaster ride: It has surged more than five times in price this year to a record just above $5,000 in early September, but in two weeks crashed by $2,000. By Thursday morning, bitcoin was trading above $4,000, up more than 300 percent for the year, according to CoinDesk .

The volatility in the value of bitcoin is one reason experts have voiced concern about investing in the cryptocurrency. Robbins says that even though some investments could make you a lot of money, they aren't predictable or steady. For him, bitcoin falls in that category.

Robbins advises thinking of investing in bitcoin like taking a trip to a casino — only bet what you can afford to lose. You might win and take home a prize, he says, but if you crap out, at least you only lost discretionary funds.

Robbins himself only devotes a certain amount of money to risky ventures and doesn't rely on them to work out. For those investments, his mentality is "I know it is just for fun I'm investing, I know I could lose, this is Vegas," he says.

For seriously planning for the future, he suggests a more stable approach: index funds.

"Index funds take a 'passive' approach that eliminates almost all trading activity," Robbins writes in his book "Unshakeable." "When you own an index fund, you're also protected against all the downright dumb, mildly misguided or merely unlucky decisions that active fund managers are liable to make."

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