How many families or other relationships does this describe?  The embers of resentment suddenly fanned into flame by a passing question or comment?  Pernicious and pointless.  I believe it was Mandela who said that resentment is like swallowing poison and hoping it will kill your enemy.

‘His son’s question had fallen like a bit of dry fuel on the embers of a long unextinguished resentment.’

Source: George Eliot, Adam Bede (Harmondsworth: Penguin, 1985 (1859)), p. 383

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