As such, the Zacks rating upgrade for FleetCor Technologies is essentially a positive comment on its earnings outlook that could have a favorable impact on its stock price. Most Powerful Force Impacting Stock Prices The change in a company's future earnings potential, as reflected in earnings estimate revisions, has proven to be strongly correlated with the near-term price movement of its stock. That's partly because of the influence of institutional investors that use earnings and earnings estimates for calculating the fair value of a company's shares.