根源 (gēn yuán): origin; root (cause)

The doctor spent several hours chatting with the patient, trying to find the root cause of his anxiety.

After years of investigation, the reporter finally discovered that the root cause of this corruption case lay in the lack of a regulatory system.

The two of them often argue over trivial matters, but the real root cause is a lack of trust between them.

The teacher believes that the main root cause of this student's poor grades is his complete lack of interest in learning.

One of the root causes of the economic crisis is excessive bank lending, which led to many people being unable to repay their debts.