To be honest, I have previously watched this film during my childhood. At first, I thought that John Nash is truly doing decryption work or spy work for the Pentagon, and when he is no longer needed, the government decided to brand him as losing his sanity and all of the work that he had done is a part of his delusions.
After rewatching the film again and again, I found out that the main message of this film is mental illness. From this film, I see that Russell Crowe managed to master the depiction of a schizophrenic person. I applaud the effort that he has done in order to make his performance believable, and especially Jennifer Connelly, for having a range of emotion that is suitable with the role of a mental illness sufferer.
Paul Bettany's performance as the 'imaginative' Charles Hansen is one that is deserving praise. Though he's only a part of Nash's delusions, he managed to break free from the bounds of Nash's mind. At one point, he was even fighting with Nash in their room and the struggle between them looked real.