Lab LCP 1.2s, field LCP 4.0s — why both are right

Lab LCP 1.2s, field LCP 4.0s — why both are right
Lab data (Lighthouse) runs one cold load on a throttled-but-clean machine. Field data (CrUX) is p75 across real devices and networks.
— Lab used a simulated Moto G4 + 1.6Mbps; your real p75 user is on a mid-tier Android with a saturated LTE link
— Lab can't see your logged-in pages, cookie-heavy states, or third-party A/B scripts that load conditionally
— The 2.8s gap was 90% slower TTFB in the field (shared hosting under load) + late-loading consent script
Fix the field number; lab is a regression guard, not a target.
Takeaway: optimize p75 field LCP, treat lab as a unit test.