major and minor machining mistakes

I made a little mistake, machining-wise, today. We are making vises and I was supposed to shave a 30 degree angle off of one end of the vise, which I did perfectly, exactly according to the print, except I shaved it off the wrong end. Oops. So that was a mistake, but then again, I did quite a few things right. In the real world, you would have to junk the part and start over, but since this is a class, we can get away with a few things.
That is one kind of mistake. A major mistake on a CNC lathe can be much worse, and much more dangerous. Computer controlled machining can seem easy, but if you program the machine wrong, it will destroy itself or cause a major amount of damage before you can stop it.