or generate more content statically during build time. Server-side rendered apps may look like they're getting pixels painted on the screen quickly, but beware of user interactions being blocked by large script executions (e.g. re-hydration to wire up event listeners).
Stop taking fast networks, fast CPU and high RAM for granted.
In some cases, third-party scripts can pre-empt first-party ones in terms of priority and bandwidth on the main thread, also delaying how soon a page is interaction-ready.