One of my favorite quotes is from Atlas Shrugged, by Ayn Rand. Well into the book, Dagney Taggert, who is Vice President of a railroad, places a man named Jeff Allen in charge of a disabled train. When he asks who he is that people would obey him, she tells him, "They’ll obey anybody who expects obedience."
I believe that the author hit on one of the ultimate truths of leadership, and am astounded that it is seldom quoted in that context. If you arrive on the scene of an incident - perhaps an emergency requiring decisive action - expect obedience. That's not the time to sidle up to somebody and make small talk about his dog. Tell - don't ask.
Expect obedience and you'll get it.