Functional Decision Theory (FDT) is a new way of making decisions that focuses on using a fixed mathematical function to determine the best course of action. FDT outperforms other decision theories like Causal Decision Theory (CDT) and Evidential Decision Theory (EDT) in various decision-making scenarios, such as Newcomb's problem, the smoking lesion problem, and Parfit's hitchhiker problem. By following FDT, individuals can maximize their outcomes and make better decisions in complex situations.