He thinks it's only natural for others to help him.
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history
This idiom comes from the ancient text《左传》(Zuǒzhuán, Zuo Commentary), where 经 and 义 referred to the unchanging principles governing heaven and earth. Over time it evolved to mean anything considered self-evidently right.
usage
Often used critically — when someone says 他觉得这是天经地义的, it usually implies the person has an entitled attitude and takes things for granted.
