laws & principles
Jakob's law
People spend most of their time on other sites, so they expect yours to work the same way. Familiar patterns are faster to use because visitors arrive already knowing them - you're borrowing every habit the rest of the web has taught them.
The demo
Two quick rounds. Each time, find and click the three parts I name in a page you've never seen - though you've met every one of its parts on a thousand other sites. One round puts them where you'd expect; the other moves the same parts somewhere odd. Both are timed.
Find and click:
What this demo shows (text version)
You're shown a mock page built from labelled regions every website has - logo, menu, search, account, basket, help - and asked to find and click three of them, against the clock.
The first round arranges those regions the conventional way; the second shuffles the very same parts into unexpected places. Most people are markedly slower the second time, even though nothing is hidden and the clicks are identical. That gap is Jakob's law: you came in already knowing where things belong - because every other site taught you - so a layout that defies the convention makes you hunt for what you'd otherwise have found on instinct.
The same parts, the same clicks - yet the rearranged layout slowed you down, because you went looking where other sites had trained your eye. That pull towards the expected is Jakob's law: convention is a head start you get for free, and break at your peril.
"Be consistent with the rest of the web" gets heard as "never do anything original", which isn't it. The point is to spend your novelty budget where it earns something - the actual job your product does - and stay boring everywhere people are just trying to get around. A surprising checkout is a lost sale, not a brand moment.
My rule: put things where muscle memory reaches for them - logo top-left and it goes home, search top-right, the basket where every shop keeps it - and save your invention for the bit no one else has. Familiar plumbing, original rooms.