I know this is very basic, but for those who dont know this, or who dont remember to use it, this is extremely valuable.
Most of us make small mistakes fairly regularly when using a computer. In most programs, you can undo the last thing that you did. Also, some programs now have "multiple levels of undo," which means you can undo the last thing you did, the one before that, and so on.
In most programs, the second menu (at the top of the screen), is the Edit menu. The first command is usually "Undo" (or "Undo <something>" where <something> is the last thing that you did). When you make a mistake, click on Edit, and click on Undo, to undo the very last thing that you did.
The Undo Command
In programs with "multiple levels of undo," if you click on Edit and Undo again, it will also undo the second last thing that you did, and so on.
I suggest that you try to associate the feeling of panic, with the words "Edit, Undo" so when you make a mistake and are panicking, you will remember Edit, Undo.
You cant undo absolutely everything, but you can undo most things, so this is very useful in practice. So when you make a mistake, remember Edit, Undo.