zhǐshàngtánbīng

Traditional: 紙上談兵

lit. military tactics on paper (idiom) / fig. theoretical discussion that is worse than useless in practice / armchair strategist / idle theorizing / cf Zhao Kuo [[趙括|赵括]] leading an army of 400,000 to total annihilation at battle of Changping [[長平之戰|长平之战]] in 260 BC