This is the second film where Zemekis explores the questions of 'Is life governed by destiny?' or 'Are we just a bunch of feathers buffetted by the erratic winds of chance?' (think opening credits of Forrest Gump, which he also directed). It is a type pop-culture nihilism:
From www.apologetics.org: "Nihilism is a pessimistic view of reality which results from "God is dead" thinking. In the words of Nietzsche, since there is no God, "there is no one to command, no one to obey, no one to transgress." Often, nihilists deny that life is meaningful or purposeful in any way, resulting in a sort of anarchistic worldview. As the French atheistic nihilist once said, "It matters not whether a man is a drunkard or a ruler of empires; in the end, both men will suffer the same fate" (Sartre). In the works of Franz Kafka and Albert Camus, nihilism is reduced to this sort of abusurdism as well, as they explore the themes of meaningless, despair, hopelessness, and the trivial nature of life itself."
In this film, like Forrest Gump, Zemekis seems to come down on the side of hopeful nihilism. We're just feathers, but that's not so bad. You make the best of what you have, and that's that. 'Why keep going?' There is no answer, and Zemekis doesn't offer one. You just keep going. You just do. But notice, there is no God, there is no grand destiny, order, rhyme or reason. As Chuck Nolan says at one point, 'I decided I just had to make it through each day, because perhaps tomorrow the tide might bring in something new.' The rest of this dialogue is a challenge to this idea; the idea of that there is something a little more hopeful than pure nihilism, but it would be a huge spoiler to put that dialogue here.
Much as I like Castaway, I tend to resist being moved by a Hollywood movie. I feel a little like I do with advertising. I feel compelled to resist the message since I know they are trying to manipulate me. That is, it's not honest art, it's purposely manipulative commerce. I'm supposed to be entertained not reflect on life. I was entertained. In fact, this is what I hate about Hollywood movies. Come on, say something honest about something, anything! Hmm, well that doesn't sell I'm sure. Soon I'll get over my entertainment break and go back to difficult subtitled movies.
I must share someone else's hilarious review of castaway. If you enjoy satire on many levels and are not put off by somewhat explicit humor, you'll probably find this funny, otherwise skip it: Castaway satire.