A site that feels quick on office fibre can be unusable out past 1604 or in a garage with the door down.
Where the page really gets opened
In a driveway in July with the phone already hot. Out past 1604 where the bars drop to one. In a garage where the signal gives up entirely.
That is where the site is judged, out on the far side of 1604, and it is nothing like the desk it was approved at. Eight seconds there hands the job to whoever managed two.
What a builder quietly ships with it
A builder must handle any arrangement a customer might invent, so it loads the whole toolkit before knowing what you used. A few service pages end up towing a layout engine, a motion library, and an icon set nobody opened.
Publishing trims none of it away. It goes out to every visitor, on every page, over the far side of 1604 included, from here on.
Photographs straight off the handset
A single shot off a modern phone runs four to eight megabytes. Ten in a gallery asks a stranger on cellular to pull down about fifty.
Through a resizer those ten total roughly four hundred kilobytes and look no different on a screen. Nothing else you can do to a small site helps this much.
Everything that got bolted on
The chat tab, the spinning testimonials, the coupon overlay, the embedded scheduler, the tracking tags, the consent notice. Each rings a different company, and the page stays half-built until all of them answer.
On a weak connection they time out one by one while the visitor stares at grey panels. Very few return more work than the wait costs.
Heat slows the phone down too
A handset that has been sitting in a truck in August throttles its own processor to cool off. It gets slower exactly when your customer needs it most.
A page that was merely sluggish in March becomes unusable in July on the same device. Building light is not a nicety in this climate.
Test it the way it gets used
Leave the phone in the truck for twenty minutes in summer, then load your own homepage on cellular and time it.
Three seconds should cover reading the opening line and finding the number. If it does not, something needs to come off the page.