Over the last two decades, hardware-based isolated execution environments, commonly known as "trusted execution environments" or TEEs, have become widely deployed [1,2,3,4]. However, concerns about vulnerabilities (like the Foreshadow attacks [5]), and potential for abuse have been persistent and have recently become increasingly pronounced. In this talk, I will discuss the history of (mobile) TEEs [6], what motivated their design and large-scale deployment, and how they have evolved during the last two decades. I will then discuss some of their shortcomings and potential approaches for overcoming them. I will also briefly touch on other types of hardware security primitives that are being rolled out by processor manufacturers and the opportunities they offer for securing computing