Undo

If you have ever done anything regrettable in life, then you'll wish you had this. It doesn't work in real life but it does work in most programs.

When you have done something you don't like, try pressing Control-Z (hold the Control key down while hitting the Z one time). Often you will be able to go back to the way things were before you did the regrettable thing. Some programs will allow you to hit Control-Z and go step by step back (as many as 32 steps back).

If Control-Z (ctrl-z to its friends, of which it has many) doesn't work, you might have to start over which is another good way of undoing something.