Thought is a scarce weapon.
Civilization advances by extending the number of important operations which we can perform without thinking about them. Operations of thought are like cavalry charges in a battle—they are strictly limited in number, they require fresh horses, and must only be made at decisive moments.
Whitehead argues that civilization progresses by automating routine tasks into habits, thereby liberating our limited mental energy for truly significant challenges. He views conscious thought as a finite, high-stakes resource that, like a cavalry charge, loses its impact if squandered on the trivial or mundane. By delegating repetitive actions to the subconscious, we preserve our cognitive "fresh horses" for the decisive, creative, and critical moments that define human advancement.