This rule sounds contrary to anything most writers have ever read or been taught. It's of course important to show everything worth showing, such as dramatic interaction and heated dialogue. But it is acceptable to tell a few things, too.
Utilize the power of description about surroundings, what's going on inside a character's head, or in the world of your story itself. Masello points out the opening of Dickens A Tale of Two Cities, "It was the best of times, it was the worst of times." So if Dickens can do it...
Also, things that don't need to be seen don't need to be shown. Who wants to read about a heroine getting ready for work? We know she'll shower, style her hair, put on makeup, get dressed, make coffee and eat breakfast.
Only show these things if something important happens to affect the story. Perhaps she slips in the shower and breaks her leg, or spills hot coffee and scalds herself, etc., etc.
Masello mentions something that Elmore Leonard, a master of pacing, once said. He keeps his books moving briskly along leaving out all the parts readers don't want to read.
Anything in your current WIP that can be told and not shown? Happy writing, and thanks for visiting!