People
Even if you are on the right track, you'll get run over if you just sit there.
— Will Rogers
Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Being headed in the right direction isn't enough on its own, says the speaker. If you park yourself on the path and wait, something moving will still flatten you. The joke is grounded in plain common sense: good direction needs actual motion behind it.
Context reviewed