"A car is useless in New York, essential everywhere else. The same with good manners"

Mignon McLaughlin's quote is a comparison between the usefulness of a car and great manners. In New York City, cars are not required due to the fact that of the substantial mass transit system. Nevertheless, in most other places, a car is important for getting around. Likewise, excellent manners are not constantly needed in particular circumstances, however they are vital in a lot of other contexts. Excellent good manners are a sign of respect and can help people to get along much better with each other. The quote is a suggestion that although specific things might not be needed in certain places, they can be essential in other locations. It is necessary to be familiar with the context and to change accordingly.