In 1993, a cognitive scientist named Don Norman joined Apple. His title was "User Experience Architect" - a phrase he coined himself, because no existing job title captured what he believed was the actual problem with software: it was designed by people who already knew how it worked, for people who did not. He wrote a book about it the year before, "The Design of Everyday Things," arguing that when something is difficult to use, the fault belongs to the design, not the person struggling with it.
That argument was radical. It still is, in practice, even if everyone now agrees with it in theory.
The Trap of Knowing Too Much
You are the worst possible person to evaluate your own design. That is not an insult - it is a structural problem with expertise. Once you know how a system works, you cannot unknow it. Psychologists call this the Curse of Knowledge: the information you carry makes it impossible to accurately simulate what it feels like to encounter something for the first time.
Think about the last time you watched someone struggle with a piece of software you use every day. You could see the answer clearly. You might have even felt impatient. That sensation - the gap between your experience and theirs - is the gap UX design exists to close. The discipline is fundamentally about transferring understanding from the designer's head into the product's structure.
This is why user research is not optional, not a luxury you pursue after launch, and not something you can replace with intuition. Every assumption you hold about how a user will navigate your product is a hypothesis. Some will be right. Many will be wrong. The ones that are wrong will cost you in abandoned checkouts, support tickets, churned subscribers, and users who quietly leave and never explain why.
What UX Actually Covers
User experience is a phrase that gets applied to everything, which means it sometimes gets applied to nothing. For this course, here is a working definition: UX is the totality of how a person thinks, feels, and behaves when interacting with a digital product, from the moment they discover it to the moment they stop using it.
That is a wide definition on purpose. It includes:
The moment someone first hears about your app and forms an expectation. The first screen they see and whether it matches that expectation. The path they take to complete a task - and every friction point along that path. The moment they get confused, the error message they read, the support page they find (or cannot find). The point at which they decide the product is not worth the effort and leave.
UX design is the practice of shaping all of those moments deliberately rather than letting them happen by accident. It sits upstream of interface design, which is the visual layer. The visual layer matters enormously, but you cannot compensate for a broken structure with a beautiful coat of paint.
Mental Models Are the Invisible Rules
Every user arrives at your product carrying a mental model - an internal map of how they expect the system to work, built from every other digital product they have ever used. When your product aligns with that mental model, the user feels fluent and capable. When it contradicts it without explanation, the user feels stupid, even though the fault is yours.
Mental models are not fixed, and they are not always rational. They are shaped by dominant conventions. If every email client in history has put the compose button in the upper left, and you put yours in the lower right, every user will look in the wrong place before finding it. You might think you are innovating. Your users will think your app is broken.
This does not mean you can never deviate from convention. It means that when you do, you are taking on a teaching cost - you are asking the user to revise their existing mental model, and you need to actively help them do that. Onboarding flows, tooltips, empty states, and progressive disclosure are all tools for managing that teaching cost. Ignoring it is how you get an app with a clever design that nobody can figure out.
Key Point: Your product does not exist in a vacuum. Users carry prior expectations from every interface they have ever touched. Design with that history in mind, not against it.
UX vs. UI: The Architecture vs. The Furniture
UX and UI are not the same thing, and treating them as interchangeable will cause you real problems. If a digital product were a building, UX is the architecture - the floor plan, the placement of doors, the logic of how rooms connect, whether the bathroom is where you expect it to be. UI is the interior design - the colors, the materials, the typeface on the signage, the lighting that makes the space feel inviting or cold.
A well-decorated building with a nonsensical floor plan is disorienting to live in. A logically organized building with depressing interiors makes you reluctant to stay. Both layers matter. But you solve them in sequence, not simultaneously. Figure out the architecture first.