Berkshire fundamentally was not a good business, he invested in a textile firm right around the time the North American textile industry started to face really heightened global competition. If I recall correctly, in '64 Buffett took control and tried to keep the thing going and had the mill invest some of its cash flow into the business, but all those investments ended up worthless as the mill eventually had to shutter. He could have deployed the capital elsewhere and earned positive returns.

Eventually (circa '67)he realized it was a lost cause and stopped investing in the mill, instead he used its cash flow to go out and invest in other companies (insurance, etc) which remain there to this day.