Scientist at The University of Toronto have discovered that you actually see things better when you are in a good mood!
http://www.news.utoronto.ca/lead-stories/people-who-wear-rosecoloured-glasses-see-more-university-of-toronto-study-s.html
So this whole complaint of positive thinking being " silly" and having "no useful purpose" is not true! In improves your ability to perceive things that people in a bad mood miss!!