The capabilities of users and hence the probability of appropriate responses can also be affected by many external factors. The part of the process with which a user interacts may be as simple as a box, or as complex as an aircraft cockpit. Users must monitor or react to the status of the process, its environment, and the effect their actions have. Displays that are difficult to see or understand increase the probability of error. Each decision must be put into action.
Users learn by the feedback they get, and use the feedback to correct errors and control the system.
Providing appropriate and timely feedback is one key to successful interface design. Prolonged or excessive physical demands can cause injury or discomfort. Establishing and taking account of the profiles of target users for the system of interest is an important step. Small design investments to improve usability may permit major reductions in life-cycle training costs. The dynamics of motivation may be a major determinant for the manner of use of a system, regardless of the design of the interface or user training.