This book by Roger von Oech was required reading at a creativity workshop I attended many years ago. I just picked it up again today and on page 165 the exercise is “Are you creative?” and you check either the box for yes or no.  A major oil company had conducted research on what differentiated creatve people from the lesser creative ones. Engineers were asked various questions and after three months of study psychologists found the differentiating factor:

“The creative people thought they were creative, and the less creative people didn’t think they were.”