Acharya Prashant explains that inner strength is characterized by the ability to prioritize duty over desire and suffering. He defines this duty as one arising from deep understanding and compassion rather than social pressure or ignorance. A strong person is not easily swayed by the greed for pleasure or the fear of pain because their understanding grants them a sense of purpose that outweighs personal comfort. This strength is measured by the degree to which one can resist old habits and distractions that previously caused them to falter.