The Call to Adventure

The Call to Adventure is just what it sounds like. The Hero has been established in his Ordinary World, and now comes the beginning of his Journey. The Call to Adventure is often issued by a Herald of some sort, bringing a new energy into the world.
I've already talked about the Herald, so I won't go into much detail regarding that.

The Call to Adventure is also called the inciting incident (you've probably heard that one from me before), the initiating incident, the catalyst, or the trigger. All these words signify the same concept of CHANGE. Yes, in all caps. CHANGE is the most important thing to get the story rolling. It's change that compels (propels? impels?) the Hero to begin his Journey. He cannot go on the way he's been getting by. He has crutches, addictions, defense mechanisms. Something happens (something a.k.a. the Call to Adventure) to make it impossible for the Hero to use these coping methods anymore. He must CHANGE or FAIL. That's the idea behind story. The Hero changes. He is "called to adventure." What is adventure? A change in the norm, a shift of lifestyle, a quest to make things better.
Before all this happens, the writer shows the Hero's tragic flaws. (Think tragic hero from ancient Greek plays.) What about my Hero is less than desirable? Personality traits--pride, vanity, recklessness, low self-esteem, hostility, sloth, quick temper, etc. Addictions--power, food or drink, bullying, shouting, passivity, aggression, etc. Wounds--a grudge, a death, a traumatic event, psychological scars, etc. There are always ways in which the Hero needs to change internally to succeed.
Besides all this, there's the obvious external Need For Change. Maybe there's a war on. Maybe someone is in grave danger. Maybe someone lost his job. For some reason, things can't go on the way they have been.
The Hero's realization of this, with or without help from a Herald or synchronicity (a series of accidents or coincidences) or a temptation, is the Call to Adventure.