The answer is the difficulty of determining what is real. Typical modernists had a loss of meaning in the modern world, so there themes included the question of "What is real?" There was a search for meaning in a world without God, and a search for self with a critique of traditional values.
1. Beatrice says that the purpose of the simplicity in her town's design is to help them forget themselves. The Abnegation have dull hairstyles and wear dull clothes, and they only eat dull food. They try to keep everything dull because they believe that forgetting yourself makes it easier to be selfless, as vanity causes selfishness.
2. When Beatrice is talking to Caleb, she hears the whistle of a dauntless train in the distance,and says that "it sounds like the Dauntless, calling me to them." She realizes that she wants to be free, and that she doesn't want to give up the part of herself that makes her Beatrice Prior. From this you can infer that she will most likely transfer to Dauntless at the choosing ceremony.
It all depends on which American Dream you're talking about.
When I Google the American Dream, a website defines it as "...the belief that anyone, regardless of where they were born or what class they were born into, can attain their own version of success in a society where upward mobility is possible for everyone."
This isn't true. It just isn't.
In a perfect world, the dream itself doesn't change, but the rules we have in place to keep specific groups of people lower than others do. I personally believe it can't. I do think it is achievable without hard work; specifically if you aren't a minority, and born into a rich family. But, this is just my personal opinion.
Internal conflict is your answer
