CNBC’s Jim Cramer suggested research can give investors an edge, stressing that it’s necessary to gain knowledge about a stock before adding it to one’s portfolio.

“You should never buy anything that you don’t have some personal knowledge about, unless the stock in question belongs to a well-known, best-of-breed operator,” Cramer said. “But for the vast majority of stocks, don’t even think about buying them unless you actually know something about the underlying company.”

When Cramer first started trading, it was harder to access corporate information than it is now, which made investing more difficult, he said. But at the same time, he continued, it was easier to gain an edge by finding data that was “buried in places that no one would ever look.”

Most material is on the internet, Cramer said, and investors can use search engines and chatbots to access any relevant information.

Cramer reflected on some of his early stock picks, including Florida-based outfit American Agronomics Corporation, which developed citrus groves, as well as women’s fashion company Bobbie Brooks. But he lost money on both investments, he continued, noting that the former dropped to nearly $0 after a flash frost in Florida, and the latter went bankrupt. Cramer said his big mistake was a lack of research. He had chosen these stocks based on articles he’d read in Forbes magazine — but that information alone was not enough reason to buy.

A little later on, he learned from a friend that Standard Pressed Steel, a local fastener company, was hiring. Cramer bought some shares and managed to make some money. The fact he learned from a friend was key, Cramer said, as it’s a good sign when a company has so much business it needs to hire more workers.

“What did I know to win in SPS? I knew something that wasn’t widely known, at least back then,” he said. “I knew they had more business than they expected. It wasn’t everything, but it was something that few outside my neighborhood would’ve known. I had an edge.”