The chief difference from other interface design philosophies is that user-centered design tries to optimize the user interface around how people can, want, or need to work, rather than forcing the users to change how they work to accommodate the system or function.

To effectively evaluate the cost and benefit of each design decision that affects the UI, you need insight across many fields, from cognitive psychology to human factors to graphic design.

Designing the UI is fundamentally an exercise in compromise—not compromise between designers and other project stakeholders (usability should never be sacrificed as a result of office politics)—but compromise between the drawbacks and benefits of design decisions. Every UI decision, from a pixel’s precise placement to the entire site’s information architecture, should be made judiciously. Careful consideration of the benefits each design decision affords and costs its users is essential. It’s the sometimes-subtle expense that many people often overlook, and every UI decision does have expense. Educated compromise across all UI decisions is essential to creating the best interface possible, and is, ironically, required if you are to avoid designing a compromised interface.