This series was supposed to be a laugher, even though the visitors had dominated at the Olympics and world championships for years. Perhaps even eight straight, particularly after Esposito beat Vladislav Tretiak 30 seconds into the game with Prime Minister Pierre Trudeau leading the cheering. And when Paul Henderson made it 2-0 at 6:32, it was party time for the 18,818 fans.

Alas, from that point a funny thing happened on the way to the Forum.
...
Soviets 7, Team Canada 3.

How could this happen? Why was it allowed to happen? What went wrong? Why?

Much of it was an outgrowth of Team Canada’s arrogance.

http://www.montrealgazette.com/sports/Summit+Series+Game+Canada+reels+shocking+loss/7176790/story.html