One example being once the phrase "sweet summer child" came up with someone asking where it originated and why it was popular all of the sudden. Some were insistent it was a common phrase in recent times prior to A Game of Thrones using it and others were saying it's always been a common thing and GoT was just the latest media but not related to its modern usage. A default ngrams search will show some decent activity in the 1800s then the phrase catching on a bit in the early 90s, staying steady through the late 90s, until it took off in the late 2000s. The phrase turns out to have definitely been said in the 1800s but maybe not with the frequency the graph might hint at initially because of the infrequency of recorded material at the time. Then unsmoothing things and shrinking the date range you'll see it really didn't take off until just after 1996 where it died down pretty quickly until 2011.

I.e. what initially looked like something that had been a common phrase before and into popularity in recent times turned out to be something that had been previously mentioned but not really in use then lines up exactly with the release dates of the book and movies for A Game of Thrones instead of something which slightly preceded it. This shows how easy it is to end up with two opposite conclusions by using Ngram Viewer slightly differently.

Alright, enough rambling about the hazards of Ngram Viewer in a post focused on Moore's Law :p.