This "training" method teaches birds to do what the larger, more physically stronger human wants it to do without allowing the bird to form any emotional bond with the bird except fear and subordination. This is the totally wrong way to "tame" a bird.
Parrots live in flocks which are held together by mutual trust and need. To win over a bird emotionally, intellectually and physically, you need to show the bird you are trustworthy and to treat it the way you want it to treat you: with respect, trust and love.