Each period is dominated by a mood, with the result that most men fail to see the tyrant who rules over them.
The quote suggests that each historical period is characterized by a prevailing attitude or mood, which can blind individuals to the oppressive forces around them. As a result, people may not recognize the tyranny that governs their lives. This lack of awareness can prevent them from questioning authority or seeking change, as they are absorbed in the mindset dictated by their era.