If you spend much time on etsy forums, you hear that everyone should have a positive attitude, all the time, ever. I'm skeptical, as I'm thinking, when do you ever craft or promote, with all this telling others how to be?
So this study amused me. Basically, folks who already felt bad felt worse when thinking positively. Personally, I know I do. Objectively, I'm a middle of the road jeweler, so I find it more useful to try to improve my skill than to think I'm awesome anyway.