As we learn more about the way the world works, our beliefs regarding acceptable behavior change. At the turn of the 20th century, no one was expected to practice household recycling, for example. Nowadays it's almost shocking if someone doesn't separate their trash.
Of course it can work the other way too, and many of today's common practices would have been horrifying back then. Check out this gallery to see which everyday occurrences would have shocked folks a century ago.