Definition & Meaning of "a man is a lion in his own cause"in English

What is the origin of the proverb "a man is a lion in his own cause" and when to use it?

The origin of the proverb "a man is a lion in his own cause" is unclear, but similar ideas have appeared in historical legal and philosophical discussions. The saying suggests that when an individual has a personal stake in a situation, they are likely to exhibit greater courage, strength, and determination than they might in other circumstances. It emphasizes that personal investment in a cause or effort often leads to extraordinary motivation, resulting in individuals putting in extra effort to overcome obstacles or achieve their goals.