Man has demonstrated that he is master of everything except his own nature.

The line contrasts humanity’s outward conquests—over tools, environments, and systems—with an inward failure: self-mastery. It suggests that technological or civilizational progress does not automatically bring moral, psychological, or spiritual development. “Nature” here points to the persistent drives and patterns that govern human behavior—fear, aggression, desire, vanity, and self-deception—implying that these remain largely unmanaged even as external power grows. The aphorism also carries an implicit warning: the more control humans gain over the world, the more dangerous their lack of control over themselves becomes, since ungoverned impulses can steer powerful inventions and institutions toward harm.