"Thomas Carlyle, the eminent Scottish essayist and sometime pphilosopher, was once scolded at a dinner party for endlessly chattering about books: 'Ideas, Mr. Carlyle, ideas, nothing but ideas!' To which he replied, 'There once was a man called Rousseau who wrote a book containing nothing but ideas! The second edition was bound in the skins of those who laughed at the first.'" -Benjamin Wiker, 10 Books That Screwed Up the World and 5 Others that Didn't Help, (2008), Regnery Publishing, p. 2.
[I do not think it right to give Rousseau too much credit for movements which may have had plenty of life without him, but I think it is good to recognize the vast consequences ideas can have].