纸上谈兵 / 紙上談兵
zhǐ shàng tán bīng
Meaning
- literally military tactics on paper (idiom)
- figuratively theoretical discussion that is worse than useless in practice
- armchair strategist
- idle theorizing
- cf Zhao Kuo 赵括 Zhào Kuò leading an army of 400,000 to total annihilation at battle of Changping 长平之战 Cháng píng zhī Zhàn in 260 BC