It’s not sure that Bobby McFerrin foresaw the results of this recent study published in the PNAS (shortly reviewed in the Scientific American), but it turns out that following his advice is really what one should do in order to become creative and to suddently have tons of great ideas. However – and here comes the really interesting part- if one would like to pursue any of those amazing ideas obtained while in a state of supreme happiness and really focus on it, s/he needs to get in the (an) opposite mood. Hence, the following law of motion might be the ideal path to success (perhaps I should patent this idea and get filthy rich): don’t worry, be happy, get angry, stay angry!
P.S. I expressly chose anger and not depression; the latter might lead you to focus on the less pragmatic ideas…