Steven, Cherrybomb is right. US audiences would like to think they could take the risk and still battle through to save the world. Most movies like that are based on long shots. And the audience loves it if the hero triumphs AFTER having had the dilemma, and sweated over it, but took the chance and put his friends first, because that's how they would subconsciosuly like it to be in real life (would that it were). And of course, all this makes it end on an upper, not a downer.
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