Warren Buffett’s Berkshire Hathaway added at least two new positions to its portfolio in the first quarter, and increased stakes in several other holdings.

Berkshire added a 10-million-share new position in General Motors to its portfolio during the quarter, as well as a new 1.6-million-share position in Viacom, according to CNBC. Based on the size of the positions, it’s likely that Berkshire managers Todd Combs or Ted Weschler were responsible for the buys, CNBC adds.

Berkshire added to seven existing positions, including IBM and Wells Fargo, which decreasing six positions, including Intel and Dollar General. Berkshire also filed some of its transaction information in confidential filings with the SEC, “often a sign Buffett is accumulating a large stake in a company but doesn’t want copycats to drive up the price until he’s done,” CNBC’s Alex Crippen writes.

Buffett also offered a number of nuggets of wisdom at Berkshire’s recent annual meeting, and  Vitaliy Katsenelson did a nice job summarizing one in a recent post on his ContrarianEdge blog. The Buffettism in question: “If you are going to choose your friends and your investments if they agree with you, you are going to have a very peculiar life.”

Katsenelson goes into greater depth on that point. “When you are long a stock you are naturally trying to seek out investors who have the same opinion, and naturally stay away from those who have contrary views,” Katsenelson explains. “Instead, we should try to do the opposite, seeking out smart people who, after doing their research (a very important point), came to a different conclusion from ours.  … When we find someone who disagrees, we need to identify exactly where the differences in opinion lie (assumptions, new/missing important data points, etc.) and then methodically and objectively try to refute those points.  If you cannot, maybe you are not as right as you thought you were.”