If you're abstaining from bitcoin because you just don't know enough about it, you're in good company.

Billionaire investor and Fisher Investments founder and chairman Ken Fisher told TheStreet founder Jim Cramer that he's not buying into the bitcoin craze even as some of his contemporaries pile in.

"Finance theory says you make money knowing something other people don't know," Fisher said. "And the fact of the matter is, I ask myself what I know about bitcoin that other people don't know and the answer is nothing. So, therefore, I don't need to do it."

Fisher subscribes to the school of thought that focuses on what must be done in order to turn a profit, not what could be done or what might eventually work. His is a theory based on what he's "gotta do," Fisher told Cramer.

"My basic goal is to keep being successful forever," Fisher said. "And to that end, I know this is a probability business, not a certainty business."

The key to best playing that "probability business" is outperforming relative to the stock market. But to meet that goal, investors have no real need to leave stocks in the first place, Fisher said. That means no bitcoin for this billionaire.

Fisher's thesis makes sense, especially given the backdoors through the stock market that could see investors gain on the rapid rise of bitcoin and its blockchain technology. Take Nvidia Corp. (NVDA) for example. The chipmaker plays an integral role in mining bitcoin with its high-tech graphics processing units -- and the company's stock has gained over 75% since the start of the year.

Fisher doesn't need to get into the bitcoin itself, he said, because he doesn't know more than the next guy. If he did, it could be reason to take a risk and invest. But since he doesn't, Fisher is watching from the sidelines.

There is what Fisher referred to as a "window pane" through which investors can now see into the bitcoin euphoria period from the bitcoin optimism period, drawing on the John Templeton theory of the lifespan of a bull market.

Templeton's theory goes as follows: "Bull markets are born on pessimism, grow on skepticism, mature on optimism and die on euphoria."

Fisher said that as skepticism surrounding bitcoin wanes, investors are migrating into the middle of the optimism period. But some keen watchers notice the final life stage of the bitcoin bull market -- euphoria -- even as optimism takes hold.

"It's the first time that people want animal spirits, John Maynard Keynes' phrase, to come alive. They want those animal spirits to go, 'Party time.'" Fisher said. People are starting to get "very, very excited."

Nvidia is a holding in Jim Cramer's Action Alerts PLUS Charitable Trust Portfolio . Want to be alerted before Cramer buys or sells NVDA? Learn more now.

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