Every second of loading costs sales: what to measure, what to fix first and why speed is a design decision.
Speed is the first thing a visitor experiences, long before your copy or your photos. On mobile, every extra second of loading loses people who were ready to buy.
Measure what people feel: Core Web Vitals tell you how fast the main content appears, how quickly the page responds and whether things jump around.
Fix the heavy things first: oversized images, third-party scripts nobody reviews and fonts that block the page. They usually cause most of the delay.
Treat speed as a design decision, not a final check: fewer elements, a clear hierarchy and one purpose per page make sites faster and easier to use.