Back in the day, like way back in the 1930s, the movie industry came up with this marketing principle called the Marketing Rule of 7. Basically, the big dogs at the studios figured out they had to repeat the same advertising and promotions to be sure that people got to watch their movies. 

This idea of repeating the same message through different channels (social media, email, in-person, etc.) is something that we often forget to do in services. We share a piece of important information once I believe that now everyone remembers this information. But the rule of seven can motivate us to communicate more often to make sure people really got the idea.

This is a first draft of a principle that might end up in a book of the "Service Design Principles" series.