"lie behind" is a phrase that conveys the idea of something being the cause or reason for a particular situation or event. Synonyms for this phrase include "be responsible for," "be the root of," "be the source of," "underlie," "cause," and "originate from." These synonyms highlight the importance of understanding the underlying reasons and causes of a situation or event, rather than just focusing on the surface-level symptoms. By identifying the factors that lie behind a particular issue, we can address its root causes and work towards finding lasting solutions.