The underlying principle of Brett Hartvigson's strategy is a thorough knowledge of the client's individual requirements. Hartvigson emphasizes that every client is unique so a one-size-fits-all approach to financial advice is not effective. Hartvigson encourages advisors to engage in comprehensive consultations to their customers, focusing on their future goals, risk tolerance, and financial history. This approach to client-centricity is not just about trust but also enables advisors to customize their strategies to meet the needs of clients, offering specific solutions that align with the financial goals of the client.