How Do You Start and End Campaigns?

"Why, yes, it is a Calabi-Yau space."
My question is really about how you think about the end of a campaign when you are starting it...hopefully that makes sense.

Do you: (a) just start and plan on playing until it fizzles out at some point? (b) Start with a time limit in mind but only a vague idea of how to end the campaign and then figure it out as you go? (c) Start with a series of options for the ending and then see which direction the players go? (d) Start with a clear destination and end in view? (e) Or is it None Of The Above?