"premature optimization is the root of all evil" -> I've found this super useful in projects. This doesn't mean you don't spend time on design or architecture,

"premature optimization is the root of all evil" -> I've found this super useful in projects. This doesn't mean you don't spend time on design or architecture, but it means many engineers have a strong tendency to jump on optimization opportunities too quickly (the more junior the stronger the tendency), AND this causes bad architecture choices that come to bite you hard later on. Keeping it simple and un-optimized is often better than early optimizing, not just because you save time and it's not worth it (hardware is cheap), but also because you keep your architecture elegant and the real bottlenecks will be different from what you thought they were and will come up later. It's absolutely valid, and wisdom that's often hard earned.