Capability is a broad concept, not limited to personal abilities.

By "fair," it simply means your dad can't take the exam for you—not that he can't help you slay fierce tigers, subdue dragons, build irrigation canals, relocate tombs, publish papers, or achieve results.

None of those latter things should be forbidden; comprehensive ability is the full picture of a person's capabilities. Comprehensive ability encompasses your family background, your heritage, your parents, and even your grandparents in every aspect.