Sia Karamalegos, a performance engineer and Google Developer Expert in web technologies, shares his insights on common web performance mistakes. He emphasizes the limitations of relying solely on Lighthouse scores and advocates for Real User Monitoring (RUM) to truly understand user experiences. Sia discusses the significance of Core Web Vitals and the challenges posed by non-Chromium browsers. He provides actionable advice for developers to enhance performance metrics and effectively utilize data for optimizing web performance.