America is an "improbable idea" that works despite the challenges.

The lines form the very first sentence of the essay "A Quilt of a Country" by Anna Quindlen.

Explanation:

The given statement or claim is from Anna Quindlen's essay "A Quilt of A Country" where she presents the American nation as a "quilt" that is formed of a bond between the numerous nationalities in it. This commentary delves into the cultural diversity of the people amidst the claim that it is a nation racially discriminating against 'outsiders'.

The given line is from the very first sentence of the essay. Beginning her commentary with the claim that "America is an improbable idea", Quindlen seems to assert that America may be unrealistic, or impossible to happen but it did happen. And not only that, it "works despite the challenges" it is faced with. And it is these "challenges" that brings the united spirit of the people, in times of "a common enemy".