The summary.
UX IS WHETHER IT SOLVES THE PROBLEM. UI IS WHAT APPEARS ON SCREEN.
A beautiful interface to something that does not solve the problem is a failure.
DESIGN IS DECISIONS, NOT DECORATION
What to include, what to leave out, what is most important, what happens when things go wrong, and what the defaults are.
Most people accept defaults, which makes choosing them well one of the highest-leverage decisions available.
THE CENTRAL ERROR
Assuming users resemble you. You built it, so you cannot judge whether it is obvious.
Design for the least confident person who must succeed, and use their vocabulary rather than your internal terminology.
EVERY ADDITION COSTS ATTENTION
Interfaces accumulate and nothing is ever removed. Ask what proportion of users need it, and whether it could be automatic instead.
DESIGN THE STATES PEOPLE ACTUALLY MEET
Empty, loading, error, and far more data than expected.
The empty state is the first thing a new user sees and is usually designed last, or not at all.
RESPECT CONVENTIONS
People arrive expecting things to behave as they have elsewhere. Breaking a convention casually makes people fail and blame themselves.
WHAT DECIDES WHETHER A DESIGN WORKS
Whether people complete the task. Watching five people attempt it reveals most problems.
