Here are three of my favorites -- I think they have shaped how I view the world.
1. In the fifties a series of studies showed that children who grew up with nightlights in their rooms tended to need glasses when they got older. So parenting advice was to avoid putting nightlights into children's rooms. But later studies re-crunched the data and what they found was that parents with bad eyes had trouble seeing in the dark and had a greater tendency to put nightlights in their kid's rooms. So the kids needed glasses not because of the nightlights, but because of genetics.
2. I remember in my psych text book's discussion of suicide they had a long discussion of the symbolism of jumping off the Golden Gate Bridge. It was the furthest point West, the end of the line, etc. Then the book noted the supreme irony that every one who jumped off the bridge jumped looking back at the city, not out towards the ocean.
Years later when I lived in San Francisco, I would walk across the bridge. I noticed that the walkway was only the city side -- so if you wanted to jump, as opposed to being hit by a car -- you had to jump facing the city.
3. There was a doctoral dissertation about the vast vast majority of American barns being painted red. It looked at the symbolism of the color red, it examined the barn colors in the various countries that emigrants came from. Finally, it concluded that barns were painted red because red paint is made from iron oxide -- in other words -- you can make it from rusty nails and it is the cheapest paint to make to cover large areas.