Who Does the Work?
Knowledge | Actions | System Weaknesses
Computer work means that user and system work together on the user's tasks. This means that there is a division of labor and responsibilities between the two. Your goal is to make the work as easy and efficient as possible for the user - and not for the system. Therefore, check what the system can do, and what has to be left to the user.
Motto: The system should serve the user, not the other way round!
Knowledge
Do not require users to enter data that the system already knows or could retrieve from elsewhere!
Example: If the user already entered parts of an address that clearly identify the time zone - like "Chicago" and "USA", why require users to enter the time zone manually?
Note: The system can remember data for the user, like the history of input values or their frequency, and provide useful default values for many fields.
Actions
Do not require users to do things that the system could do for them.
Example: Do not let users enter the VAT if the system can calculate it.
System Weaknesses
Do not let users suffer from system weaknesses!
Example: "Zero indicator" - Users were required to set a "zero indicator", because the system could not distinguish between the entry of a zero and no entry.
Example: Provide templates for "formatted" data such as dates, times, and so on.
Source: Simplifying for Usability