This and Taking Shelter both suggest (SPOILERS)
...that mental illness can be overcome by an act of will, motivated by love for those close to the person suffering delusions.
As far as I know, there's no basis for this in reality. To suggest that a delusional person could get over it if only he wanted to enough or had the right people supporting him is just untrue. It also suggests that if someone doesn't overcome their illness that they have failed somehow.
It's a nice message for a story, but it doesn't speak to the truth about mental illness.