Forgiveness is a design principle that helps people prevent errors, minimize consequences, or allows them to correct their mistakes. It may include warnings, confirmations, help or assistance, safety nets, and a way to reverse the error.
Example: Road sign warning drivers that there are pedestrians are not paying attention to traffic.
Designing warnings in computer applications help prevent errors like downloading an unknown file or deleting a file forever. However, warnings should be limited because repeated warnings can lead to user annoyance and frustration. Allow users to opt out of warnings once they have learned the system.
Example found online: Google Apps provide a safety net for users by autosaving their work. Users don’t have to think about saving.
Affordances and constraints help prevent errors. For instance, the size of gasoline nozzles are constrained and regulated to match the size of the afuel tank opening in cars. This prevents users from putting diesel gasoline into their car that only takes unleaded gasoline.
Example found in the real world: MacBook plug. The plug is attached to the laptop with magnets. It unplugs easily if the user trips on the cord.
Forgiveness contributes to the happiness of users because it makes them feel secure and safe.
In my opinion, forgiveness is one of the most important principals of design, especially in this age that we all trying to multitask which in turn increases the amount of errors. I liked your google apps example. I always thought that forgiveness is that cancel button when user accidentally deleting a file or the message that pops up in the MS Word when a user is trying to close a document without saving the recent changes.