Core Web Vitals matter less for ranking than for revenue
Core Web Vitals are a ranking signal. They are also a weak one — Google has repeatedly described page experience as a tie-breaker between results of similar relevance, not a primary factor.
This gets read as "so it does not matter". That is the wrong conclusion, for a reason that has nothing to do with rankings.
The three metrics
Largest Contentful Paint — when the main content appears. Target under 2.5 seconds.
Interaction to Next Paint — how quickly the page responds when touched. Target under 200ms. This replaced First Input Delay and is considerably harder to pass, because it measures every interaction rather than the first.
Cumulative Layout Shift — how much things move as the page loads. Target under 0.1. This is the one users notice most viscerally, because it is what makes you tap the wrong thing.
Why to care anyway
Slow pages are abandoned. That effect is much larger and much better evidenced than the ranking effect, and it applies to every visitor regardless of where they came from.
For paid traffic it is worse: you paid for the click, and abandonment before render is money spent on nothing. A landing page that takes four seconds on mobile is wasting a fixed percentage of every campaign.
Field data, not lab data
Lighthouse gives you a lab score from one simulated run on one device. Search Console and the Chrome UX Report give you field data from real visitors on real devices and connections.
These disagree constantly, and the field data is the one that counts — for ranking and for reality. A site can score 95 in Lighthouse and fail its Core Web Vitals assessment because actual users are on worse phones and worse networks than your test.
The usual causes
LCP — a large unoptimised hero image, render-blocking resources, or slow server response.
INP — heavy JavaScript on the main thread, frequently third-party scripts including tag managers with too much in them.
CLS — images without dimensions, ads or embeds injected above existing content, and web fonts causing reflow.
That last group is worth noting: the tag container, the consent banner and the chat widget are among the most common causes of poor scores, and none of them are your site's code.