What happens during those few milliseconds (or seconds) of loading between the white browser and the “perfectly loaded” page? What happens if a data is missing, if a server takes time to respond, responds to an error, a missing resource, etc.? Designing these "forgotten cases" greatly improves designer/developer collaboration on performance topics. Avoiding errors, empty screens or components with layout shifts also greatly improves user experience. Let’s talk about how to design for performance, perceived performance, for those forgotten cases and beyond, like for offline, background sync, etc.