Brett Whitely on being asked "where do you get your ideas?" is reputed to have replied "I think of them".
I have no idea of the authenticity of this but when Albert Einstein was asked to respond to the same question by George Sylvester Viereck in 1929, as reliably reported in Walter Isaacson's highly acclaimed "Einstein, His Life and his Universe", Einstein responded a little more thoughtfully;
"I'm enough of an artist to draw freely on my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world."
And for Nassim Nicholas Taleb's take on the subject;
"Intelligence without imagination: a deadly combination".