Sometimes the actual deletion must occur before a mistake is realized. I have often seen undo implemented as a 'soft' delete which means the read-side needs to

Sometimes the actual deletion must occur before a mistake is realized. I have often seen undo implemented as a 'soft' delete which means the read-side needs to be 'undo aware'. Sometimes undo is implemented by backing up all related data to a separate location which is also non-trivial. Managing the 'restore' half needs logic to account for conflicts and changed state. It doesn't change the fact that Undo is an amazingly useful feature but its not always as simple as 'delay the action'.