Amgen's market-beating ways are unlikely to evaporate any time soon.Few stocks consistently outperform the vaunted S&P 500 index due to its inherent advantages in diversification and stability. This benchmark index draws its strength from a broad portfolio of America's top companies, allowing it to weather individual sector downturns and capitalize on various market trends simultaneously.Individual stocks, in contrast, are subject to company-specific risks and industry cycles. Even well-managed companies ca ...