You can't have both the fish and the bear's paw - you can't have it all.
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Anchored in Mencius (《孟子·告子上》): 鱼,我所欲也,熊掌,亦我所欲也,二者不可得兼 - 'Fish I desire, and bear's paw I desire too, but the two cannot be had together.' The phrase 不可兼得 has become a fixed metaphor for trade-offs.