In Ernest Hemingway's novel, The Sun Also Rises, the quote "'Yes," I said. "Isn't it pretty to think so." represents the ideological beliefs of those who were a part of America's lost generation. The context puts the protagonist, Jake, in a position of not being able to have sex. This, in turn, makes his possible relationship with a woman, Brett, impossible to have. This lack of physical consummation results in the conflict invoking the quote. Brett states that they would have had a "damned good time together" and Jake replies. The interaction at hand represents the conflict between the ideological views of the lost generation and the harsh truth of reality.
Due to the war, many Americans who fought became disenchanted with America as a whole. This resulted in a mass exodus to Europe, where many felt they could live their lives in piece. They also felt that they could escape all the problems of life by running away from them.
The ideology is that without the war the world would have been a perfect, ideal place for them. Even with the war occurring, the ideal ending would have been without Jake's accident. Although, Hemingway seems to push that even with the war not existing, or existing with a different outcome, the world would not have fit the dream world the generation wished. Their own lifestyles perpetuated what happened, so even with different events, the end result could have been similar.
The truth of the times was that many of the lost generation permitted much of what happened to them in Europe to continue too far. In the situation between Brett and Jake, Brett permitted her own acquaintances to increase in number to the point where there were many men clambering to know her. When Brett was engaged to Mike there were men, even then, trying to get to know her. Robert Cohn for instance was continuously questioning Jake about Brett whenever they were together. This proved that those wishing for a better world did little in their own power to try and change it for the better.
Overall, the quote embodies the truth about the situation in Europe at the time. People were wishing for a better world, yet doing nothing to actually help it. Brett's statement shows the ideological side, while Jake's shows the factual.