Two principles of user interface design should be remembered. First, users do not like to feel trapped by the computer. Second, despite what has been done to improve the interface, users will find ways to make errors. Therefore, in order to increase the user's feeling of being in control, the system should offer the user an easy way out of as many situations as possible. Examples include:
Users quickly learn to rely on the existence of undo, so it should be made available throughout the system as a generic command that undoes a special category of user actions. These functions encourage users to perform exploratory learning since they can always try out unknown options, knowing they have the ability to get out of trouble without repercussions.
Visibility is especially crucial for exits and the undo function because users will need these mechanisms when they are in unfamiliar territory and are afraid to lose data if they do the wrong thing. A system should never capture users in situations that have no visible escape.