纸（zhǐ）paper
上（shàng）on, above
谈（tán）talk about
兵（bīng）troop. Here refers to the art of war
网（wǎng）net. Here refers to the internet
战国时期，赵国有一位名将叫做赵奢。他曾多次以少胜多（yǐshǎoshèngduō. Use little to win over many），大败（bài. Defeat）入侵（rùqīn. Invading）的秦国。
During the Warring States era of China, there was a famous general in State Zhao, named Zhao She. He defeated a much stronger state, Qin, in multiple battles.
他有一个儿子叫做赵括，他从小熟读兵法，谈起兵事来父亲也难不倒（nánbùdǎo. Not too difficult for me to fall down）他。
He has a son named Zhao Kuo. Zhao Kuo read extensively on the practices of war from a young age. When it comes to the art of war, even his father cannot win a debate over him.
后来他也被委任（wěirēn. Be appointed as…）为将军。在长平之战中，他只知道照兵书领军，不知道变通（biàntōng. Be flexible），导致全军大败，他也被箭射身亡。
Later, he was also appointed as a General. In the Battle of Changping, he lost the whole army due to his lack of practical experience. He was also killed by arrows.
后来，纸上谈兵就用来指哪些理论知识（lǐlùnzhīshi. Theoretical knowledge）强硬（qiángyìng. Strong, solid），却不懂实践（shíjiàn. Practice in real life）变通的人。
Nowadays, ‘talking about the art of war on paper’ is used to refer to people who have strong theoretical knowledge but cannot apply and make adjustments in reality.
比如说：“这个政策虽然好，政府却根本无意（wúyì. Have no intention to do sth.）推行（tuīxíng. Carry out, implement），一切都是纸上谈兵。”
For example, ‘This policy is good, but the government has no intention to exercise it, it’s all on paper.’
不过现在到了信息化时代，很多人都开始用网络代替了纸质书本来汲取知识，而“网上谈兵”也比“纸上谈兵”有了多一层意思。
Now we come to the information era, many people use the internet instead of paperback books for knowledge, and ‘talking about the art of war on the internet’ has an extra meaning compared to ‘on paper’.
有一部分网民藏在屏幕后面夸夸其谈（kuākuāqítán. Make big speeches），不遗余力（bùyíyúlì. Do not reserve any effort）地对公众人物、热点新闻、家长里短等等发表自己的见解，却不会对自己有同样严格的分析，也更不会用自己的真实身份去评价同样的东西。
Some internet users can make big speeches hiding behind the screen. They use every effort to share their opinions about public figures, trending news, family gossip and etc., but they would not practice the same kind of scrutiny over their life, and certainly would not make the same announcement in real life.
所以“网上谈兵”会被用来讽刺那些以网络的匿名性作为武器，去随意评价他人的“键盘侠”。
So ‘talking about the art of war on the internet’ can be used as a sarcasm against those internet trolls, who weaponize the anonymity of the internet and judge people all they want.