To demand something firmly and repeatedly, often in a way that won't accept 'no' for an answer.
From Latin 'insistere' (in- 'upon' + sistere 'to stand'), literally meaning 'to stand upon.' The metaphor is of standing firmly and stubbornly on something until you get your way.
When you 'insist' on something, you're literally 'standing upon' it—like you've planted your feet and won't budge. That's why we describe stubborn people as 'standing their ground,' which is the exact same metaphor!
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