Stubbornness is the strength of the weak.
Johann Kaspar Lavater (1741-1801) Swiss theologian and poet.
Obstinacy is the sister of constancy, at least in vigor and stability.
Montaigne (1533-1592) French philosopher and essayist.
Obstinacy is the result of the will forcing itself into the place of the intellect.
Arthur Schopenhauer (1788-1860) German philosopher.