FXAIX tracks the S&P 500, aiming to mirror the performance of the largest US publicly traded companies. As a broad market representation, its performance is closely tied to the US economy's health and macroeconomic factors like interest rates, inflation, and GDP growth. With a vast asset base and cost-effective structure, it benefits from scale and diversification across industries. Securities lending adds income, potentially enhancing returns. Investors should watch US economic indicators for its impact on the fund's performance.