Chance discovery is to notice and explain the significance of a chance, especially if the chance is rare and its significance is unnoticed. Chance discovery is essential for various real requirements in human life. The paper presents the significance and the achieved methods of chance discovery. Fundamental discussions of how to realize chance discovery extracts keys for the progress of chance discovery: communication, imagination, and data mining. As an approach to chance discovery, visualized data mining methods are shown as tools aiding chance discoveries.