It's true: a mind is a terrible thing to waste. Yet that's what we do when we spend our weekend -- and neurons -- reliving a workplace squabble, spend a family visit chewing over childhood issues, or spend hours beating ourselves up when someone brings one of our own long-held (but never worked on) ideas to fruition. This kind of obsessing gets us, like a hamster on a wheel, nowhere. But as noted creativity expert Eric Maisel asserts, obsessing productively...