Designed for Use: Create Usable Interfaces for Applications and the Web
Don't Make Me Think, Revisited: A Common Sense Approach to Web Usability (Voices That Matter)
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User Friendly: How the Hidden Rules of Design are Changing the Way We Live, Work & Play
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High usability is very important when it comes to websites or interfaces where users are trying to complete a task. But if we want to encourage people to play or want to be experimental, making something that violates all usability rules and is deliberately anti user friendly can actually increase engagement (see Principle 29).
Irene Pereyra • Universal Principles of UX: 100 Timeless Strategies to Create Positive Interactions between People and Technology (Rockport Universal)
Nothing important should ever be more than two clicks away
Steve Krug • Don't Make Me Think: A Common Sense Approach to Web Usability, 2nd Edition
Two of the most important characteristics of good design are discoverability and understanding.