How GA4 works
GA4 records everything as an event. A page loading is an event, a form submitting is an event, a video reaching a milestone is an event, and each one carries parameters that describe it — the page, the referrer, the value, whatever you choose to send. The older Universal Analytics model, with separate pageview, event and transaction types, is gone; there is one shape of data and you decide what fills it.
A property holds one or more data streams — a website, an Android app, an iOS app — and the web stream issues the measurement ID that identifies your site to Google’s tag. Some events arrive without any work: enhanced measurement collects scrolls, outbound clicks, site searches, file downloads and video engagement out of the box. The ones that matter to a business, such as an enquiry or a purchase, have to be sent deliberately, usually through Google Tag Manager, and then marked as key events so they appear as outcomes rather than as ordinary traffic.
Above that sits a reporting identity that stitches activity together from the device identifier, a logged-in User-ID where you supply one, Google signals where it is enabled, and modelled estimates for the gaps left by consent choices and blocked cookies.
Why GA4 matters
For most businesses it is simply the free analytics everyone has, and it is what Google Ads reads when you import goals or build remarketing audiences. Getting it wrong quietly corrupts bidding as well as reporting.
The model also suits how people actually behave now. Someone reads on a phone during a commute, returns on a laptop at work and enquires from a tablet at home. A pageview-shaped tool struggled to describe that; an event stream with an identity layer at least attempts it, and is honest that part of the answer is modelled.
Common mistakes with GA4
The first is installing it and assuming that is the job. Without deliberate events, GA4 reports traffic and nothing about outcomes, so every conversation ends in sessions.
The second is marking too much as a key event. If a scroll, a click and an enquiry all count as outcomes, nothing is an outcome and automated bidding learns from noise.
The third is expecting the numbers to agree with other platforms. GA4 counts a session, Google Ads counts a click and attributes it to the click date, and Search Console counts an appearance in results. They are three different measurements and they will never reconcile.
The fourth is naming events casually, so a year later the property holds several near-identical names for the same action and no one can safely delete any of them.
How to act on it
Write down the events and parameters before building anything, in plain language: what happened, what you want to know about it, what the business calls it. Implement them through Tag Manager, verify each one in DebugView, and only then mark the genuine outcomes as key events.
Review the data retention setting, link Google Ads and Search Console, and turn on the BigQuery export early if you may ever want raw data, because it does not backfill. A structured GA4 setup is far cheaper to do once than to unpick after a year of guesswork.