Where can you find American idealism in the novel The Great Gatsby?

The green light at the end of Daisy's dock symbolizes American idealism, the belief in the American Dream: that one can have it all—the money, the house, the girl one loves—if one only works hard enough and believes it. When Nick first sees Gatsby, "[Gatsby] stretched out his arms toward the dark water in a curious way, [and] he was trembling. Involuntarily, [Nick] glanced seaward—and distinguished nothing except a single green light, minute and far...

The green light at the end of Daisy's dock symbolizes American idealism, the belief in the American Dream: that one can have it all—the money, the house, the girl one loves—if one only works hard enough and believes it. When Nick first sees Gatsby, "[Gatsby] stretched out his arms toward the dark water in a curious way, [and] he was trembling. Involuntarily, [Nick] glanced seaward—and distinguished nothing except a single green light, minute and far away [...]." For a long time, this light is all Gatsby sees of Daisy, its visibility the only connection he has to her. And the fact that green is often associated with money—”and money is a vital part of both the American Dream and Gatsby's particular dream of winning her back—is likewise relevant.

Further, at the novel's end, Nick again considers "Gatsby's wonder when he first picked out the green light at the end of Daisy's dock. He had come a long way [...], and his dream must have seemed so close that he could hardly fail to grasp it." This line more explicitly links the light to Gatsby's, to many Americans', dreams of a better life, the best life they can imagine.

Moreover, Nick says, "Gatsby believed in the green light, the orgastic future that year by year recedes before us. It eluded us then, but that's no matter—to-morrow we will run faster, stretch out our arms father . . . . And one fine morning— So we beat on, boats against the current [...]." Despite the fact that the dream seems to get farther away from us each year, eluding us time and time again, we continue to chase the dream, continue to hope that some day we will catch it, just as Gatsby hoped. However, the implication is that we will never be able to catch it, and so our continued hope amounts to idealism only, not realism.