Overzealous People in History

In every era of history, there have been people who were overzealous. These people are often thought of as fanatics or zealots. They are single-minded in their pursuit of a cause or belief, and they are often willing to go to extreme measures to achieve their goals. Overzealous people have been responsible for some of the most momentous events in history, both good and bad. But what motivates someone to become overzealous? And why do they maintain such intense dedication to their cause, even in the face of adversity?