Bounce rate climbs sharply as load time increases past roughly 2-3 seconds, and that effect compounds on mobile. A visitor who bounces before the page finishes loading never saw your offer, your pricing, or your CTA — the best copy on the page is worthless if nobody waits for it to render.
Largest Contentful Paint measures how fast the main content feels ready. Interaction to Next Paint measures how responsive the page feels once someone tries to use it. Cumulative Layout Shift measures how much the page jumps around while loading. Translate each one to "does this frustrate a real visitor" and the metric stops being abstract.
Unoptimized hero images, too many third-party scripts (chat widgets, analytics, ad pixels loading synchronously), and web fonts blocking render are the three most common culprits — none of which require a rebuild to fix, just attention.
Budget for performance the same way you budget for design — as a feature with a measurable business outcome, not an afterthought fixed when someone complains. See our web development service if your site needs this.