Making users happy is a goal that unifies everyone on the team. The key then is to establish metrics that reflect user happiness. In the world of performance, we haven’t always done a great job of this. Often, performance metrics track how our pages are built which might not be correlated with a joyous user experience, and we start optimizing our stack for the sake of optimizing our stack. Luckily, momentum is building around UX-centered metrics such as start render time, time-to-interact, and first meaningful paint. Steve Souders discusses these new metrics that help us build web apps that produce the fast, joyous experiences our users want.