Limitations of Multi-access Activation

Multi-access activation implies high density of acceptable user actions, therefore many user errors are accepted as legitimate actions.

Example

For example, if the user of MS-Word depresses Ctrl+z instead of Shift+z (a typical key substitution error) then MS-Word cannot tell that the key combination is from a user error. Unaware of undoing the last update, the user typically continues typing, resulting in the update missing from the text.

If the users have various options to try, the system becomes complex and difficult to learn and to use. Learning slows because:

The users have fewer chances to activate any of the controls, and
Due to the increased rate of action errors, the mapping from intention to action is not consistent and the rate of negative feedback increases.

Example

Shortcut keys are a primary source for unintentional operator's faults, of which the operators are not aware .