“Wise men speak when they have something to say, fools speak because they have to say something”
Often attributed to Plato, it cannot be found in any of his writings ( see this http://languagelog.ldc.upenn.edu/nll/?p=796). The quote is attributed to Plato in A Dictionary of Thoughts: Being a Cyclopedia of Laconic Quotations from the Best Authors of the World, Both Ancient and Modern (page 560) by Tryon Edwards.
Misattributed
Source: Chasm City (2001), Chapter 12 (p. 197).
“You don't write because you want to say something, you write because you have something to say.”
Notebook E: Epigrams, Wisecracks, and Jokes https://books.google.com/books?id=NIhKY8SpAE4C&q=%22You%20don%27t%20write%20because%20you%20want%20to%20say%20something%3B%20you%20write%20because%20you%27ve%20got%20something%20to%20say.%22&pg=PA123#v=onepage, edited by Edmund Wilson (1945)
Quoted, The Crack-Up (1936)
“It's simple to be wise. Just think of something stupid to say and say the opposite.”
“It's so simple to be wise. Just think of something stupid to say and then don't say it.”
