You’re going to learn how to find a fulfilling career. You’re going to learn how to better navigate life’s big-moment decisions and kill your “wicked problems” dead. How? By training yourself to think like a designer. That, anyway, is the premise of “Designing Your Life,” a class taught at Stanford University (the school’s “most popular class,” according to Fast Company magazine) as well as the just-published book that grew out of it, “Designing Your Life: How to Build a Well-Lived, Joyful Life” (Knopf).