UnitedHealth Group stock has been rallying on news that Berkshire Hathaway has invested in the business. Warren Buffett is the CEO of Berkshire Hathaway and the investment could be seen as a possible vote of confidence in UnitedHealth's business.

Warren Buffett emphasizes that while achieving success is exciting, effectively correcting mistakes when they occur is equally critical for businesses.

Berkshire Hathaway’s portfolio added six new stocks, including the three new secret stocks. Warren Buffett was a net seller of stocks for the eleventh straight quarter.

Berkshire Hathaway ( BRK.A -0.05%) ( BRK.B 0.24%) is considered by many to be a reliable stock for long-term investors. It's outperformed the S&P 500 ever since a young Warren Buffett took over the company in 1965, and its evolution from an aging textile maker to a diversified conglomerate churned out millionaire-making gains.

The conglomerate sold Apple shares during the second quarter, though the iPhone maker remains Berkshire’s largest stockholding.

Shares of UnitedHealth Group are surging before the market open Friday as Warren Buffett’s Berkshire Hathaway disclosed that it recently purchased shares of the beleaguered insurer

Like Amazon CEO Andy Jassy, keeping a positive attitude helps the Warren Buffett-backed leader stay motivated toward success.

Berkshire Hathaway recently filed its second-quarter 13F form, revealing its stock holdings at the end of June.