Why does Hans Castorp remain at the sanatorium for seven years?

Hans Castorp remains at the Davos sanatorium for seven years because he discovers he has symptoms of tuberculosis shortly after arriving for what was intended to be a brief visit.1

Beyond the medical necessity, his extended stay represents a profound shift in his life. Castorp abandons his normal existence to immerse himself in introspection and the study of the complex political, cultural, and scientific ideas of 20th-century Europe through interactions with other patients. Ultimately, the sanatorium serves as a "magic mountain"—a space that reflects the dangers and possibilities of the outside world—where he remains until the outbreak of World War I forces his departure.1