When you can't drive. Someone who dosen't have the skills to drive a vehicle or the money to buy a car. They can either be poor, suffer from some kind of mental illness or just be so slow they can't obtain a driver's license. Can also apply to hippie types but these are less common.
Sonny and M. Rehmeyer are carless due to their terrible financial struggles, lack of an education and epilepsy and or other sorted mental disorders.