Positive thinking can be dangerous
boston.com
boston.com
Best to stay somewhere in the middle, be aware of reality, try your best to improve the situation and don't berate yourself too much if it doesn't work, pick up the pieces, learn and try again.
Similarly people who have been convinced to act happy may have problems that are just as big, but they are more pleasant to be around.
There are real benefits to positive thinking. However cancer survival doesn't seem to be among them. (Citation: http://www.cbsnews.com/stories/2007/10/22/health/webmd/main3...) And certainly when someone loses their job in a bad economy, it is downright dangerous to push a message that can be misread as, "It's your fault for being unhappy about it."
There is a balance to be reached. And our society is far too far off on the "la la, be happy" end. (Disclaimer: I am a person who is naturally inclined to be happy most of the time.)
Before someone starts throwing around "Godwin's Law", you should actually go and read a bit about Hitler's life, a serious optimism is one thing that comes across very strongly, from early on, through WWI and his time as a pretty revolutionary, to his decisions in WWII.