Why is it difficult to hold a school bag having strap made of thin and strong string?

Explanation

it is difficult to hold a school bag having a thin strap because the pressure on the shoulders is quite large , this is because the pressure is inversely proportional to the surface area , the larger will be the pressure on the surface , in the case of a thin strap the contact surface area is very small Hence the pesseure exerted on the sshoulder is very laarge .