…opposing the other four fingers is the distinct evoluted part of our body that makes us different from the  monkey and that has been making possible the building of what the humans has built during their history.
As cooking we can – actually should – use our thumbs in different actions.

Placing and pressing the thumb on the potato – or apple or any other food -, and holding the knife with the other four fingers, the hand becomes a lever. 
With a dosed pressure, and calibrated movements of the wrist, Michelangelo could carve the David out of a big single block of white marble. Peeling a potato doesn’t take such an effort.Just remember that your hand is perfect tool and that it come become a lever.

Same method to strip the zest of an orange.

In this position you can control the pressure and you can stop at istant.  No risk of cutting yourself.

Cooking means also this: finding how to use your hands with coordinated movements.