Great post Peter. Clear expectations are the foundation upon which all management (and then leadership) is built.

To answer your question - I believe the first thing that prevents the majority of managers from setting expectations as clearly as they need to is...that the expectations are clear - to them. They understand it, they asked if there are questions, everyone sat mutely, so they assume it's understood. I can almost guarantee that it is not.

What we say is not what is heard. It makes sense in our head, but not to others. Your assumptions are not their assumptions.

Effective managers check for understanding at every step. eg:  "So what do you understand the expectations to be?"  That way you know that they know...because they said it.

Thanks for a great post!