2012.12.30
In my opinion, positive thinking should be limited to application to trivial matters. An example of good positive thinking is "If it is sunny tomorrow, we will go on a picnic." It has a definite time tag "tomorrow" and is not up against another possible positive thinking, "If it is rainy tomorrow, we will still have some fun playing cards and video games indoors."
A potentially harmful example is "I will be rich by making my business a roaring success." A typical positive crap, isn't it? It does not have a time tag, probable does not finish the cycle it has started, and is very likely to become a case item.