Acharya Prashant explains the concept of weakness as defined in the Bhagavad Gita, clarifying that it does not mean a lack of physical strength or the inability to complete a task. Instead, weakness is the failure to decide to do what is right despite knowing it is correct. He emphasizes that success or failure in an action is irrelevant; what matters is the resolve to perform the right action without being deterred by the fear of consequences. This fear of outcomes, such as failure or loss of reputation, is the root of weakness. He encourages performing actions with full intelligence and strength, leaving the results to take care of themselves.