Berkshire Hathaway CEO Warren Buffett doesn't care how well the companies he's invested in did last year — he's more concerned with how they perform over decades.

"We've made a lot of money in stocks over time," he told CNBC's Becky Quick during an interview on "Squawk Box" in February. "But there's been years when we've lost money, too."

While he expects Berkshire to come out ahead over time, "we haven't got the faintest idea what years we'll be up or down," he says.

Buffett chooses companies that he believes will perform well long-term, regardless of how they're doing at any given point. This "buy and hold" strategy is one he has reiterated time and time again. When deciding if he should put money into a company, longevity has always been a major consideration.

"We sort of know it when we see it," Buffett said during the Berkshire Hathaway 2017 Annual Shareholders Meeting. "It would tend to be a business that for one reason or another we can look out five or 10 or 20 years, and decide that the competitive advantage that it had at the present would last over that period."

Because of that, he doesn't pay attention to the news when making investment decisions.

"I'm not buying them because I think they're going to go up the next day or the next week," he told Quick in February. "We watch the prices of things we do more than current events."