In "Oh, the Places You'll Go!" by Dr. Seuss, the sudden realization moment occurs when the protagonist, referred to as "you," realizes that life is not always going to be easy and that there will be challenges and obstacles along the way. This realization comes when the protagonist encounters the Waiting Place, a location where people are stuck in a state of inaction and indecision. The sudden realization is that waiting for things to happen or for someone else to make decisions will not lead to progress or success. This moment prompts the protagonist to take control of their own life and make choices that will lead them to new places and experiences.