However nice a plan looks, if it can't be carried out it's just a clay ox and wooden horse.
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From 《关尹子·八筹》: 譬如见土牛木马,虽情存牛马之名,而心忘牛马之实 - clay oxen and wooden horses look like the real thing but can't plough or carry. Used to call out things that have the name without the function.