ISO defines usability as "The extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use."
The lack of Usability causes frustration.
Usability is a Human specific factor.
More Information#There might be more information for this subject on one of the following:
- Password Authentication is Broken
- Password Periodic Changes
- Password Quality
- Password Statistics
- Public Key Infrastructure Weaknesses
- User Experience