Many market commentators will try to explain why the stock market kicked off 2019 with the best January in decades, but CNBC's Jim Cramer stressed on Friday that the move wasn't tied to historical patterns or the calendar.

"You know why stocks had such a good start this year? For the same reason they had such a bad end last year: our Federal Reserve chairman," Cramer said on "Mad Money."

The longtime market-watcher referenced the Fed Chair's remarks in October 2018, when he suggested that he was willing to raise interest rates more quickly than may have been needed in order to slow the rate of inflation.

"In December, though, Powell realized that he had been reckless," Cramer said. "There were other forces doing the job of keeping inflation down for him, so the Fed could afford to be less aggressive. That's why, sometime after the Christmas bottom, he made up his mind to let those forces play out."

On Jan. 4, Powell officially reversed course, telling the American Economic Association that the Fed "will be patient" with its rate increases and take a more data-dependent approach.

"That's why the rallied almost 8 percent last month," Cramer said. "It had nothing to do with the calendar."

Investors have to remember that, when it comes to the stock market, history seldom repeats itself, the "Mad Money" host said. That's why he worries about market-watchers who try to "gin up" patterns in the stock market, because they tend to lead people astray.

"I say each year stands on its own. I don't know a soul who predicted that disastrous December we just went through," he said. "This was a nauseating, out-of-nowhere, and, most of all, short bear market, and it was very much the Fed's creation. Almost no one saw it coming because no one thought the Fed would do what it did. In fact, all I heard going into the fourth quarter was the opposite: when the market's doing well for the year going into September, you're going to end the year strong. Another useless so-called truism."

"So hold your ears when commentators who should know better blather on and on about non-existent relationships between the stock market and the months or days of the year," he continued. "Their confidence in the calendar and 'history' is misplaced, they'll be proven wrong, and they will never, ever, ever admit that they were wrong or that their hubris and ignorance cost you money."