General Principles

• Doherty Threshold - Productivity soars when a computer and its users interact at a pace (<400ms) that ensures that neither has to wait on the other.
• Every Page Has a Hero - Any given presentation of information should consist of one primary user goal that stands out.
• Fitt's law - The time to acquire a target is a function of the distance to and the size of the target.
• Hick's Law - The time it takes to make a decision increases with the number and complexity of choices. 
• Jakob's Law- Users spend most of their time on other sites. This means that users prefer your site to work the same way as all the sites they already know. 
• Law of Prägnanz- People will perceive ambiguous or complex images as the simplest form possible, because it is the interpretation that requires the least cognitive effort of us. 
• Miller's Law (Seven plus or minus two) - The average person can only keep 7 (plus or minus 2) items in their working memory. 
• Occam's razor - Among competing hypothesis that predict equally well, the one with the fewest assumptions should be selected.
• Pareto Principle - For many events, roughly 80% of the effects come from 20% of the causes. 
• Parkinson's Law - Any task will inflate until all of the available time is spent.
• Peak-End Rule - People judge an experience largely on how they felt at its peak and its end, rather than the total sum or average of every moment of the experience.
• Progressive Disclosure - Advanced or rarely used features to a secondary screen, making applications easier to learn and less error-prone.
• A Sense of Place - Humans need to have a sense of environment, direction, and available tasks to accomplish their goals.
• - Separation of Concerns - software should be architected in a way that ensures each piece is separated from the others based on the kind of work it performs. For example, business logic should be in a separate project from interface logic, because the business logic is not dependent on the interface logic and vice versa.
• Serial Position Effect - Users have a propensity to best remember the first and last item in a series.
• Set users up for success - Provide users the ability to avoid errors; don't provide them an interface that invites failure then chides them for failing.
• Staged Disclosure - Staged disclosure is a variant in which users step through a linear sequence of options, with a subset displayed at each step. Wizards are the classic example of staged disclosure.
• Tesler's Law (The Law of Conservation of Complexity) - For any system, there is a certain amount of complexity that cannot be reduced.
• Von Restorff Effect (The Isolation Effect) - When multiple similar objects are present, the one that's the most different will be most likely to be remembered.
• Zeigarnik Effect - People remember uncompleted or interrupted tasks better than competed tasks.