The ohnosecond (https://en.oxforddictionaries.com/definition/ohnosecond) is the split second when you realize you've made a terrible mistake. Your stomach sinks, your trembling hands lift from the keyboard and you freeze. This moment of horror could be deleting a customer's records, emailing what you really think of your boss directly to your boss, or hitting "buy now" on 111 items, when you really wanted one.

The best apps allow users to back out of such actions, either with undo controls or by giving users the ability to edit actions before they're final. Google's Gmail has had an optional "undo send" feature for quite some time. This stores your sent message in a "buffer" for 20 seconds, giving you that short grace period to cancel sending. If you just ignore it, you know the message will be sent shortly. This particular feature has saved me many times.

Users will feel more in control of your product because knowing they can undo every action and recover from mistakes will free them to experiment more with the product and hopefully get more from it.

From a UI perspective, a nice pattern is to include the UNDO control on a banner (or toast) that appears after an action. The user is informed that their action worked, they see a recap of what the action was, and they're given a quick shortcut to reverse that action.

Be forgiving because people make hundreds of mistakes every day and your users will love you if your product saves their ass just once.