Looking at the relative calorie values of different foods radically changed my eating habits. Especially realising how high calorie 'boring' things like rice and bread were, vs. 'fun' things like bacon. Good example chart here.
Woah. Instead of potato chips, I could be eating an equal amount of bacon.
I'm never going to eat another potato chip again.
There's a lot of background mess in our mental pictures of the world. We try and be accurate on important issues, but a whole lot of the less important stuff we pick up from the media, the movies, and random impressions. And once these impressions are in our mental pictures, they just don't go away - until we find a fact that causes us to say "huh", and reassess.
Here are three facts that have caused that "huh" in me, recently, and completely rearranged minor parts of my mental map. I'm sharing them here, because that experience is a valuable one.