The ADP National Employment Report is a significant economic indicator that can influence investor sentiment regarding the health of the U.S. economy. Since SPY tracks the performance of the S&P 500, which is closely tied to economic conditions, lower than expected job growth could lead to concerns about economic slowdown, potentially causing short-term volatility in SPY's price. However, the impact may be moderate as the miss is not significantly large and other factors also influence SPY's performance.