usability - Deletion: Confirm or Undo? Which is the better option and why?

Which one is the better option and why?

Delete with Confirmation [The action cannot be undone]

or

Delete with one click [And provide option to Undo]

Answer

The site Good-UI argues for Undo: Try Undos instead of prompting for confirmation.

Imagine that you just pressed an action button or link. Undos respect the initial human intent by allowing the action to happen smoothly first and foremost. Prompts on the other hand suggest to the user that he or she does not know what they are doing by questioning their intent at all times. I would assume that most of the time human actions are intended and only in small situations are they accidental. The inefficiency and ugliness of prompts is visible when users have to perform actions repeatedly and are prompted numerously over and over - a dehumanizing experience. Consider making your users feel more in control by enabling the ability to undo actions and not asking for confirmation where possible.

I would tend to agree. Respect the user's ability to rationally think through and perform the action they intended. But give them the opportunity to pull back if necessary.

This isn't to say that confirmation dialogs are never appropriate. It depends on the situation. The inability for the system to retract an action is, of course, one reason to use a confirmation.

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Doesn't work as well as:

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Here are some other examples of where an "Undo" action is used in place of a confirmation.

Gmail

Gmail has a Labs feature that allows you to undo a send action on an email.

In reality the system simply delays the actual send action and allows the user to retract the request before the send really happens. But to the user this doesn't really matter -- Gmail's ability to magically recall (in short history) an e-mail I accidentally sent is all I need to know.

OSX (and Ubuntu) File Delete

When you delete a file in OSX, most of the time you don't get a dialog box asking you if you are sure. You actually take a "Move to Trash" action. In this instance you can undo the action by restoring the file from the trash (just like the physical world metaphor this action is modeled after).

This changes when you attempt to delete a file from a network drive, or other location where OSX can't move the file the trash can. In this case you do get a confirmation window telling in, very plainly, that if you continue you will never see the file again.