The best way to lose a digit before dinner is by holding the knife the wrong way
Grip the handle close to the blade and pinch the blade between your index finger and thumb. Curl your index finger if it’s long enough to feel like it might get caught underneath the blade. Get ready to chop without quivering in fear.
IN this pic you see that the section of your fingers should be straight up and down or vertical to cutting board.
Professional chefs hold both sides of the blade with the handle tucked under their wrist, from which vantage point it is impossible to slice one's finger off . Sadly, this is more common than one would think on the television