I'd be careful about interpreting that. Can you "build" numbers? Yes, in one sense. No in another. And he doesn't specify whether being able to build something

I'd be careful about interpreting that. Can you "build" numbers? Yes, in one sense. No in another. And he doesn't specify whether being able to build something is sufficient for understanding it or merely necessary. And even when you've built it, what about other ways that it could be built? If you implement binary search iteratively, then perhaps you understand binary search. But do you understand its recursive implementation?