A plain-language explanation
PageSpeed Insights is a Google tool that analyzes website performance on mobile devices and computers based on laboratory data and available data from real users.
Where it helps in practice
PSI combines a lab test with available real-user data, so its two result sets may differ without contradiction.
The decision before implementation
Choose template and device, record test conditions and fix user-impacting causes rather than chasing a score.
How to verify the result
Monitor Core Web Vitals over time, release regressions, asset weight and functional side effects.
