The defense takes a lot of persistence

In The Electric Woman, Marabel Morgan, an author of self-help books for married women, wrote, "Persistence is the twin sister of excellence. One is a matter of quality; the other, a matter of time."

Why did she not make it excellence is the twin sister of persistence? Or one is a matter of time; the other, a matter of quality?

This is an excellent defensive deal because it requires persistence on the part of the defenders. They have to take six tricks to defeat two spades. How can they do it after West leads the heart ace?