Misunderstanding about the usefulness of insight regarding mundane affairs is easily cleared. It is like bringing a printed page before a lamp: the lamp's light is not concerned with the individual words, but rather clarifies the whole of what appears on the page. Similarly, although insight is not concerned with the lesser faculties, the illumination it provides enables the latter to deal far more effectively with everyday affairs.
-- Notebooks Category 20: What Is Philosophy? > Chapter 4: Its Realization Beyond Ecstasy > # 190