Most metastatic cancers are incurable—a fact that underscores the limitations of our existing paradigms for understanding metastasis. In this Review, we use breast cancer to explore many of the enigmas revealed by these existing paradigms. Traditionally, metastatic models describe metastasis as a unidirectional process, whereby cancer cells leave a primary tumor and unidirectionally seed metastasis in regional lymph nodes or distant sites. By contrast, recent data indicate that metastasis is a multidirectional process whereby cancer cells can seed distant sites as well as the primary tumor itself. This later process, known as 'self-seeding,' has been validated in diverse experimental models. Here, we show that the self-seeding model may answer many of the mysteries inherent to cancer metastasis. Indeed, reframing our understanding of metastasis within the self-seeding model offers new opportunities for prevention and cure of metastatic cancer.