September 3, 1967 is a day known as Dagen H (H day) in Sweden. On that day, all car traffic was switched from driving on the left-hand side of the road to the right side. It was the most significant logistical event to date, in the history of Sweden.

In the not too distant future, we may have what could be known as Q Day—the day in which quantum cryptography renders large swaths of traditional cryptography broken. In Cryptography Apocalypse: Preparing for the Day When Quantum Computing Breaks Today's Crypto (Wiley 978-1-119-61822-5), author Roger Grimes has written a remarkable book on how to prepare for that fateful day.