Why it matters
Knowing the difference keeps diagnosis accurate: a beautiful site people can't navigate has a UX problem no restyle will fix, and an ugly-but-clear tool needs UI love, not another restructure. Buying the wrong fix is the common (and costly) confusion.
How it works
UX work researches users, maps journeys, structures content and tests flows: largely invisible when done well. UI work designs the visual system: type, colour, components, states. In good teams they're one conversation: the interface expresses the experience design.
What to do about it
When something underperforms, watch a user before briefing a designer: if they're lost, it's UX; if they're unconvinced or the thing feels cheap, it's UI. Then brief exactly that.
