Most programs have the ability to under the last change that was made. Some programs will even let you undo multiple mistakes. I have a few programs that will undo all the way back to the beginning of the project. No matter how far back a program will let you go, it will certainly let you get there by pressing Ctrl-Z.
You can even undo something you have typed into a form in your browser. If you are like me and make a lot of mistakes, Ctrl-Z can get you back on track fast.
If you get carried away and undo too many things, Ctrl-Y will redo what you just un-did.
TSPY=1.14