What does the spinning top represent?
The spinning top is Cobb's totem, which originally belonged to Mal. In addition to telling Cobb whether or not he is dreaming, the top represents Cobb's connection to Mal, which he cannot allow himself to give up. The top also conveys the blurred boundary between reality and dreaming that claimed his wife's life after she committed suicide in reality, thinking that it would wake her up. Cobb's decision to leave the top behind in the final scene of the film symbolizes the fact that he finally has closure about his wife's death and no longer needs to keep her memory alive in dreams.
Why is architecture important in the film?
Architecture is important in the film because the dream-worlds that the characters inhabit need to be carefully designed and constructed based on prior research. Moreover, they need to be designed and constructed in such a way that keeps the team safe from hostile projections, which is why Cobb has Ariadne practice drawing mazes and labyrinths before allowing her to build dream-worlds. The architecture and design of dream-worlds also involves painstaking attention to detail, so that the dreamer does not realize that he or she is dreaming and preemptively wake up.
Why can't Cobb go to the United States?
Cobb cannot return to the United States because he is wanted for killing his wife Mal. Cobb admits to Ariadne that, after spending fifty years with Mal in "limbo"—unconstructed dream space—he "incepted" the idea in her mind to wake up so that they could be with their children again. However, Mal continued to believe that she was in a dream, and killed herself upon waking by jumping from a hotel window, thinking that she was still dreaming. The mysterious circumstances of Mal's death cause the police to think that Cobb was responsible for her death.
Why do dreams in the film look like reality?
Inception explores the idea that dreams seem real for as long as they are happening. As a result, there is a seamless visual relationship in the film between reality and dreaming—so seamless that characters must carry around small objects called totems that let them know they are awake. The "hyper-real" veneer of dreams causes characters like Mal to question the nature of reality. Cobb encounters an old man in Mombasa who questions whether he can know with certainty whether or not he is dreaming. The ending of the film also pushes the viewer to question whether Cobb has definitively woken up, or is still immersed in a dream.
Why does Cobb tell Ariadne never to build dreams from memories?
When giving Ariadne a primer on the rules of dream-sharing technology, Cobb stresses that she can never use memories to build dream-worlds. The viewer comes to learn that, despite his own advice, Cobb uses his own memories to dream on a regular basis in order to interact with his deaf wife, Mal. Cobb's feelings of guilt, which prompt him to live inside of his memories of Mal, destroy him emotionally and threaten to compromise the mission. Thus, Cobb tells Ariadne to avoid using memories to build dreams because he knows firsthand how psychologically damaging it can be.