Don’t look away while doing this.  I heard Martha Stewart say this while explaining how to slice potatoes uniformly on a mandoline.

If you’re unfamiliar with the instrument, it’s best that you listen and watch carefully as someone else slices with it.  As I watched the cooking school, I thought back to the one time I used the instrument to slice potatoes.  I cut a nice chunk of skin because, inexperienced, I was moving too quickly, cutting too deeply, and cutting too closely the potato’s end.  It became a painful metaphor for many things.