Is this [Ivanka Trump] Chinese proverb real? —“Those who say it can not be done, should not interrupt those doing it”
NPR did a pretty good article covering this.


  After Ivanka Trump Quotes 'Chinese Proverb,' A Hunt For The Proverbial Author : NPR
  
  
  Ivanka Trump's quote of a Chinese proverb — "Those who say it can not be done, should not interrupt those doing it." — prompted a search for the original source. Mandel Ngan/AFP/Getty Images
  
  On the eve of her father's meeting with North Korean leader Kim Jong Un, Ivanka Trump seemed to be calling on her inner Yoda as she tweeted:
  
  "Those who say it can not be done, should not interrupt those doing it."
     -Chinese Proverb    
  
  Neat quote. But it was the first daughter's attribution to "Chinese Proverb" that sent social media sites into overdrive in China, where people scrambled to find who, among their ancestors, actually said this. 
  
  
  After presidential adviser Ivanka Trump tweeted what she called a "Chinese Proverb," many in China (and beyond) tried in vain to track down the quote's author. Twitter/Screenshot by NPR
  
  After a thorough search of the Analects of Confucius, Taoist texts and everything in between, nothing definitive has come up. But that hasn't stopped millions of Chinese social media users from making wild guesses like these, straight from Weibo, one of China's most popular social media sites:
  
  
  临渊羡鱼不如退而结网 — It's better to knit a fishnet instead of standing by the river and hoping for fish. 
  观棋不语真君子 — Don't give advice while watching others playing a chess game. 
  勿以善小而不为 — Don't ignore small acts of kindness simply because they seem trivial. 
  己所不欲，勿施於人 — Don't force others to do things you don't want to do yourself. 
  吃不到葡萄说葡萄酸 — If you haven't tasted the grapes, don't say they're sour. 
  
  
  A lack of a clear source for Trump's tweet has some people speculating the first daughter either made it up or, a more likely explanation, cut and pasted the saying from an unreliable website. In the meantime, the search for this "proverb" through ancient Chinese texts has become something of a viral Quixotic quest in China, filled with many a sarcastic comment:
  
  
    "Did you get that from a fortune cookie?"
    
    "估计是 fortune cookie 上学来的..."
    
    "Don't mistake something as a Chinese proverb simply because it's written in Chinese characters."
    
    "不能因为某句话上面配了个鬼画符的"中国字"，就觉得那是句中国谚语。——鲁迅"
    
    "Many foreigners make up Chinese proverbs much like we make up English ones."
    
    "都想多了。其实，很多欧美人说的中国谚语，都是他们自己编的，如同我们也编了他们的不少谚语。"
    
    "I think Jack Ma said that."
    
    "我想是马云说的。"
    
    "A Chinese proverb from Ivanka has killed the brain cells of Chinese netizens."
    
    "伊万卡一句中国谚语，累死了全中国网友脑细胞啊。"
  
  
  And finally, a tweet from an actual Chinese literature scholar, Brendan O'Kane:
  
  "You can call any old [s***] a Chinese proverb on the internet."
    — Confucius   
  
  Who knows? Maybe someday one of these might become a Chinese proverb, too.