“It's not a problem to put it up, It's a problem to take it down.”

As quoted in The Ultimate Guide to Celebrating Kids : K-6th Grade School (2005) by Linda LaTourelle, p. 134

“The Pattern of Inquiry” from Logic: Theory of Inquiry
Logic: Theory of Inquiry (1938)
Variant: It is a familiar and significant saying that a problem well put is half-solved.

Source: The Subtle Art of Not Giving a F*ck (2016), Chapter 5, “You Are Always Choosing” (p. 97)

Bush will add more than 20,000 troops to Iraq http://www.cnn.com/2007/POLITICS/01/10/iraq.bush/index.html CNN (January 11, 2007).

Source: Six Impossible Things

A New Model of the Universe (1932)

According to The American Chesterton Society http://www.chesterton.org/qmeister2/19.htm, this quotation is actually a paraphrase by John F. Kennedy http://en.wikipedia.org/wiki/John_F._Kennedy of a passage from The Thing (1929) in which Chesterton made reference to a fence or gate erected across a road: "The more modern type of reformer goes gaily up to it and says, "I don't see the use of this; let us clear it away." To which the more intelligent type of reformer will do well to answer: "If you don't see the use of it, I certainly won't let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it."
Misattributed

Source: Fuzzy sets and fuzzy logic (1995), p. 2-3.