Berkshire Hathaway's portfolio and operational improvements demonstrate fundamental strength that contradicts its 15% underperformance versus the S&P 500 over the past year.

"Amazon's shares have underperformed the S&P 500 index in recent months, setting up a very attractive buying opportunity."

"Berkshire Hathaway shares have remained almost unchanged this year, while the S&P 500 has returned 14.5% through August 14. However, the company's large cash reserve gives it enough room to keep investing. Its portfolio also has lower valuation and debt levels, along with stronger returns on equity than the S&P 500."

"Berkshire Hathaway has underperformed the S&P 500 by over 15% in the past year, despite portfolio outperformance and operational improvements."