Warren Buffett made a strategic error by not selling Coca-Cola despite its price rising from $1.3 billion cost basis to $28 billion market value, because after Gen Re acquisition diversified Berkshire's portfolio in 1998, Coke only compounded at 4.5% annually (2/3 from dividends) rather than the 36% annual returns in the first 10 years, making it unworthy of its massive portfolio weight given margin and growth stagnation.