"Intelligence is a tool. If you use your intelligence to rationalize being incurious because you already know everything, or use your intelligence to find more sophisticated and convoluted reasons why what you decided was true before you began thinking is still true, you are not being very smart. Smart and stupid are not innate characteristics, but rather products of a willingness to educate oneself, to ask for and seek help from those smarter than oneself, and to mark one’s beliefs to market."Brad DeLong at the Washington Center for Equitable Growth http://equitablegrowth.org/2013/11/29/970/understanding-the-stability-of-general-equilibrium-as-a-requirement-for-getting-a-union-card-as-an-economist-friday-focus
It's unfortunate that Prof. DeLong slips into economese in the last sentence, which makes an otherwise brilliant and universal quote a little less so. For those who don't regularly follow DeLong, his phrase "mark one's belief to market" means revising beliefs that are proven wrong by world that is, and not living in the world as you imagine.