Mobile first
They're standing
on a train
The person tapping your link has one hand free and forty seconds. Everything — the page, the product, the checkout — is built to work in that, not on a desktop nobody's using.
A phone propped against a cup on a café table
Two taps to buy
Card payment without an account to create first.
Fast on bad signal
Pages are static and small, so they arrive before patience runs out.
Readable one-handed
Type, spacing and buttons sized for a thumb.
Storefronts are statically rendered, so they load from a cache rather than a server round trip.