system
A chat on subreddit /r/me_irl
human
This thread is so weird. Pretty much ***everybody*** knew that McDonald's was bad for you. That's not why Supersize Me was a hit. It was the visuals. It's like knowing that cigarettes can kill you vs. watching a documentary showing a person literally dying of lung cancer. 
 
Nobody had their eyes opened in the sense of "Until I saw Supersize Me I thought McDonald's was okay," they had their eyes open in the sense of "I knew it was bad for you, but I didn't ***know*** it was bad for you." 
 
Edit: that, and the time frame. None of the poor health effects he suffered were surprising. Everyone knew eating fast food all the time would cause the problems he suffered. However, a lot of people were surprised at *how fast* the problems were.
gpt
Yep, you explained it better than I did. 

If people need a current analogy, look at vaping. 

So many kids do it, because it's cool. And it would be very uncool to say you're concerned about the long term ill-effects, frankly some of the coolness is because people exhibit a careless attitude towards it. 

I'm sure if pressed on the matter, all the kids would admit they know it's likely to be bad for them. But they don't really wanna find that out, they'd rather keep the knowledge at arms length than really see exactly what it's gonna do to them.