Past tense of reap: to harvest or gather a crop, or to receive a benefit or consequence as a result of an earlier action.
From Old English 'ripan' originally meaning to gather or harvest grain. The metaphorical sense 'to receive consequences' developed from the agricultural meaning (you harvest what you planted).
The phrase 'reap what you sow' is so old and fundamental to farming that it became a core moral metaphor across cultures—the idea that actions have predictable consequences comes straight from agriculture.
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