There are a couple of news items that overlap in their conclusions: quality of life is crucial in determining our positive or negative state of mind.
One is about pigs: an experiment demonstrated that pigs living in rich environments consider an unknown new sound suggestive of something positive, like a treat, while those living in a poor quality environment, thought of the new sound as likely to mean something rather negative or useless. In other words: they are driven towards optimism or pessimism by their quotidian reality. Full story at Science Daily.
The other one is about people. Researchers, studying 300,000 people from around the globe, found that having good friends and neighbors enhances survival by 50%. Having few friends is as harmful, it seems, as being alcoholic or a heavy smoker, and more harmful than being obese or not exercising. They warn that our modern lifestyle rather tends to destroy such crucial social networks so important to our well being. Full story at BBC.