Ankur Moitra opens MIT's 18.200, Principles of Discrete Applied Mathematics, with a rundown of course logistics before turning to the pigeonhole principle. He states the basic idea, that if more objects than containers exist then some container must hold more than one, then works through surprising applications where the principle resolves problems that look nothing like counting at first glance. The lecture closes with an introduction to the foundations of probability, including how sample spaces are constructed and why they matter for later topics in the course. Moitra teaches at the board with a direct, example-driven style, building intuition before formalizing definitions. At 74 minutes, this is a full first session rather than a preview, aimed at students beginning a rigorous discrete math sequence.