How does the fact that resources are not equally substitutable across uses affect the production possibilities curve?

Question

Quizplus · Accepted Answer

The production possibilities curve will be bowed outward because resources are not equally substitutable across uses, indicating that as the production of one good increases, the opportunity cost of producing an additional unit of that good increases, leading to a concave shape from the origin.

How Does the Fact That Resources Are Not Equally Substitutable