I’m honestly sick of seeing people blame the Next.js App Router for being “slow.” Next.js is insanely fast — the problem is we keep shipping bad architecture: massive client bundles, redundant round trips, and we opt out of optimizations Next hands us for free. In this video, I walk through the five mistakes I keep seeing when I review real codebases (including student projects), and I fix each one with changes you can measure. First, I show you how to stop guessing and start measuring: run a bundle analyzer (Turbopack or webpack) and find the real culprits. Then we kill the “use client” virus by pushing client components down to leaf nodes so you don’t accidentally ship your entire page to the browser just to support one button. After that, I fix server-side slowness caused by accidental data waterfalls (sequential awaits) by fetching in parallel with Promise.all and/or splitting fetches into components with Suspense boundaries for streaming. I also cover a sneaky one: fetching the same data twice for SEO metadata and for the page render — and how to fix it with React cache or Next’s use cache directive. Finally, we handle what users actually feel: stop turning pages into client components for spinners (use loading.tsx), optimize images with next/image + sizes, and eliminate layout shifts by using next/font instead of manually importing Google Fonts.