Before you do any shopping this week — either in-store or online — take 35 minutes to listen to this episode. We're with Dan Ariely, professor of psychology and behavioral economics at Duke University. He discusses his book, Dollars and Sense: How We Misthink Money and How to Spend Smarter, and answers: Why does paying for things often feel like it causes actual pain? When is a sale not really a sale? In Mailbag, investing in your early 20s and how to broach estate planning with your parents.