Nvidia's lofty expectations are starting to come into question.Nvidia (NVDA -9.53%) has been the source of some incredible gains in both 2023 and 2024. However, some savvy investors are starting to sell, just in case Nvidia can't live up to the lofty expectations built into the stock. These investors include some billionaire hedge fund managers, such as David Tepper, who runs Appaloosa Management. Is it time to follow suit? Or is there more upside for Nvidia?Billionaires are starting to take profitsIf a por ...