This document presents the famous Monty Hall problem, which is a probability puzzle that most people initially get wrong. It involves a game show with 3 doors, where a prize is behind one door. A contestant picks a door, then the host opens an empty door from the other 2. The contestant is then offered a choice to stick with their initial door or switch to the other unopened door. Most people think the chances are 50/50, but in reality the chance of winning is higher (2/3) if the contestant switches doors due to the information provided by the host eliminating one door. The document uses several examples and explanations to thoroughly illustrate why the probability favors switching doors in this counterintuitive puzzle