What event marks the beginning of "The Metamorphosis" by Franz Kafka?

The beginning of "The Metamorphosis" is marked by Gregor Samsa's transformation into a giant insect. This event is crucial, as it not only sets the tone for the entire narrative but also serves as the catalyst for the story's exploration of alienation, identity, and the human condition. The shocking nature of this transformation forces both Gregor and his family to confront the implications of his new reality, leading to a series of events that highlight the disconnection between Gregor’s previous life and his current state. This abrupt change effectively establishes the surreal atmosphere that is characteristic of Kafka's work and serves as the focal point around which the themes of the story develop.