Sometimes as DMs we plot out the direction of our campaigns. Players being players, if you give them any sort of freedom it is doubtful they will follow the path of least resistance.
How do you know when your campaign is over?
Player apathy? DM apathy? Player goals reached? Just feels like it? The itch for something new?
I will freely admit as a DM I probably have about 6 months before the next great campaign idea hits me - usually for my players, the desire for change lags behind my own.
When is the right time to bring your campaign to an end, and is it necessary to have everything tied up neat in a bow, or can it end like the second book in a trilogy, with more stories to be told, but in this case no one to tell them?