The world would resist his changes because a person's destiny wasn't independent. Their destiny was intertwined with many others, and any changes to a single destiny would set off a cascade of effects in many others.
Because of the resistance of the world, even something as simple as killing a chicken with the Destiny of Fate Supreme Metac was complicated and could be difficult.
A chicken belonged to someone. Even if the owner was a mortal farmer, the fact remained that he would affect the mortal farmer too if he touched the chicken.
The destiny of the chicken was to be sold by the farmer. The person who bought the chicken would kill it, stew it, and use it to celebrate a family event. The family members at the event would eat the chicken soup and have another reason to live another day and not commit suicide.
