The challenge of norms.

Treehugger has a post on the insensitive banter to police officers had when covering an accident scene where a jogger was critically injured by a truck while running to work.

A man jogging in West Seattle was struck by a semi truck, and was critically injured. According to eyewitness accounts, the man was broadsided by the truck, was flung into the air, and landed on his head. Barely clinging to life, cops arrive on the scene--and proceed to mock the man, who for all they knew was dying, for not driving a car.
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(from the Seattle Post Intelligencer - The accident took place during the extended closure of the Alaskan Way Viaduct, when the state Department of Transportation was urging commuters to bike, walk, or take a ferry to work in order to avoid a traffic gridlock.

The normal of driving is such that incidents like this convince parents not to let their kids walk or bike to school. This in turns creates the belief in kids that cars are the only way to get around and they cannot wait to get a drivers license as soon as they can. The challenge in life is to understand that there are other ways possible.