‘究其原因’ is a formal, literary verb phrase meaning 'to examine the root cause' or 'to investigate the underlying reason.' Literally, 究 means 'to investigate thoroughly,' 其 is a possessive pronoun ('its' or 'the'), and 原因 means 'cause' or 'reason.' Together, the phrase conveys a deliberate, analytical effort to uncover the fundamental source of a situation—not just surface symptoms. It often appears in written Chinese, academic writing, news reports, and formal explanations.

This expression is typically used at the beginning or middle of a sentence to introduce a causal analysis. It implies intellectual rigor and objectivity, and is rarely used in casual speech. While it can apply to any domain (e.g., social issues, technology failures, or personal decisions), it’s especially common when discussing problems with complex origins—such as public health crises, economic trends, or environmental changes—where superficial answers are insufficient.