Motivation and habit
Delighters
Also called Attractive quality, Excitement features
Unexpected touches that please people but aren't missed when absent, unlike basics, which only get noticed when they fail.
Features don't all affect satisfaction the same way. Basics cause anger when missing and earn no thanks when present; performance features please in proportion; delighters surprise people and stick in their memory.
Delighters fade into expectations over time, so yesterday's surprise is today's basic. Check that the basics are solid before investing in delight: a charming animation doesn't make up for a lost file.
In practice
An email app that notices you wrote 'attached' but forgot the attachment, and asks before sending.
Common mistake
Adding delight to cover broken basics. People don't remember the confetti; they remember the crash.
Where it comes from
From the Kano model, published by Noriaki Kano and colleagues in 1984, which calls them attractive quality.