The later Buddhist tradition considers ignorance ("avidya") to be the root cause of samsara. Avidya is misconception and ignorance about reality, leading to grasping and clinging, and repeated rebirth. According to Paul Williams, "it is the not-knowingness of things as they truly are, or of oneself as one really is." It can be overcome by insight into the true nature of reality. In the later Buddhist tradition "liberating insight" came to be regarded as equally liberating as the practice of "dhyana". According to Vetter and Bronkhorst, this happened in response to other religious groups in India, who held that a liberating insight was an indispensable requisite for "moksha", liberation from rebirth.