Constraints limit the possible actions that can be performed on a system. For example, dimming or hiding options that are not available at a particular time effectively constrains the options that can be selected. Proper application of constraints in this fashion makes designs easier to use and dramatically reduces the probability of error during interaction. Constrains simplify usability and minimize errors.
The Director of Design at Stuff Creators Design in Houston and author of the best-selling design book, Universal Principles of Design.