纸上谈兵

zhǐ shàng tán bīng

armchair strategy

Character by character

纸zhǐ
paper

上shàng
on

谈tán
discuss

兵bīng
warfare

没有实际经验，再好的计划也是纸上谈兵。

Without real experience, even the best plan is just armchair strategy.

Tone: negative (criticism).

From the Records of the Grand Historian: Zhao Kuo knew all the war manuals yet led Zhao to disaster at Changping.

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