纸上谈兵 (zhǐ shàng tán bīng): lit. military tactics on paper; fig. theoretical discussion that is worse than useless in practice; armchair strategist
纸上谈兵
lit. military tactics on paper; fig. theoretical discussion that is worse than useless in practice; armchair strategist
Zhao Kuo could recite every treatise and lost the army anyway. For theory from someone who has never done the thing.