cognitive psychology
Von Restorff effect
When one item in a list is noticeably different from the others, it sticks in memory far better than its neighbours. Distinctiveness is a memory signal: the odd one out earns attention it didn't ask for.
The demo
Scan this list once, don't try to memorise it, just read through it.
Which item stood out from the rest?
What this demo shows (text version)
A list of ten items appears, nine of which are styled identically and one of which is rendered in a contrasting colour and weight: the isolate. After the list is hidden, the reader is asked to pick which item stood out.
The vast majority choose the isolate correctly, even without any deliberate effort to memorise it. This is the Von Restorff effect (also called the isolation effect): an item that differs from its context is encoded more strongly, without the reader deciding to pay it extra attention.
You noticed, and remembered, the one that was different. That's the Von Restorff effect doing exactly what it promises.
Designers exploit this constantly: a green "Start free trial" button in a row of grey links; a red "Delete" action among blue ones; the single bold price on a comparison table. The brain is wired to log discontinuities, so distinctiveness serves double duty as both attention-getter and memory-anchor.
It cuts the other way too. In a list where everything is highlighted, nothing is. The effect only works because contrast is relative: make one thing louder, not everything louder. Designs that scream for attention everywhere end up remembered for nothing.