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First and foremost, Casey's (and through her, the film's) relentless optimism, enthusiasm and indomitable hope for a better future. Although almost the entire world has given up and embraced their imminent demise, hope still remains, and there are those willing and able to fight for it no matter the odds. And as it turns out, this hope is all it needs to snap humanity out of their self-destructive depression. Really makes you wish it were that easy in Real Life.
Casey leaving a message for her father while on her way to Frank Walker's after the incident at Blast From the Past. She let her father know she is alright and apologizes for sneaking out.
Athena revealing after she is critically hit to save Frank that she had always considered Frank special and made it her mission to reinvigorate his optimism.
The last words of wisdom Athena gives to both Casey and Frank: "Dreamers must stick together".
Frank's answer to a question from one of the newly built recruiters how they would identify candidates using the parameters given to them. It shows despite still being cautious about the future that he had rediscovered his optimism and tells them that Athena did more than just follow a program with zeroes and ones.
