Ian Ball opens MIT's course 14.12, Economic Applications of Game Theory, with the building blocks that game theory rests on before any strategic interaction enters the picture. The lecture covers individual decision-making: how to model preferences, utility functions, and rational choice under certainty and uncertainty, the groundwork needed before introducing other players into the analysis. Ball works through the formal setup economists use to describe an agent choosing among options, connecting the mathematics to the intuition of what it means to act rationally. Running fifty-seven minutes, this first session of the fall 2025 course sets up the vocabulary and assumptions that later lectures will extend into genuinely interactive settings, where one person's payoff depends on what others choose. It is a methodical, blackboard-style introduction aimed at students about to move from individual optimization into strategic games.