One kind: known destination, known route.
“Does this bus stop at 82nd street?”
It does or it doesn’t; it’s for you or it’s not.
The other kind: unknown destination, unknown route.
“I’m building a rocket ship.”
Two different journeys — with very different vehicles, costs, and questions. A rocket probably won’t get you to 82nd street, and a bus won’t get you to Mars.
Colin Steele 