Any way you look at it, the man who calls himself Prot is a stranger in a strange land.

Prot (Kevin Spacey) claims he is an extraterrestrial on a fact-finding mission, which explains why he is currently a visitor at a Manhattan psychiatric hospital. At first it's just a few patients who believe in Prot, but eventually he wins over the whole ward plus a few of the staff and even confounds some of America's leading astronomers.
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The people who made K-PAX seem to assume that audiences have the brains and the gumption to work out their own conclusion to the mysteries raised in the movie.

So this maybe-alien story ends with the filmmakers refusing to wrap things up in a tidy little package and answering all your questions. Ambiguity reigns.
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