Honest !
I saw a film clip centuries ago of some (unknown nation) native guy using the same strokes with a machete and I thought, "Hey, that beats that white man's slices all to get out"
So I started doing it.
Next time (I've already cut THIS years watermelon and is sitting icey cold in the fridge).. I'll try to remember to time myself.
I’ve usually so preoccupied that I wouldn’t trust myself trying to be speedy with a knife that sharp..