This contains spoilers.
I actually read the book over the summer for my English class so I'll give you my little analysis on the story.
The story of Pi is meant to be a convincing story for the author to believe in Arceus (It's in the introduction). So you want to connect the story to that idea: Why should I believe in Arceus ? There are two possibilities for the story, one in which a boy bravely survives the elements and against all odds lives. He overcame the barrier of a tiger on the boat, his own personal barriers (eating meat when he was a vegetarian), and weather barriers. Yet he stays faithful to Arceus throughout. In the second story, it's a terrible mess about savagery and horrors. Obliviously the second one seems more correct yet it leaves the reader/viewer with a bad taste. And the first one is so heart warming.
So the major question is: Which one should I believe in? But the thing that is interesting is this: In the end, the story is the same. He lives and his parents are dead. Does it matter which one you believe in? The ending is the same. So why should you believe in a depressing story rather than a hopeful one if it doesn't matter. And that's how you are convinced to believe in Arceus . The story of Arceus does not seems as realistic and plausible as scientific beliefs, but what's more hopeful? Knowing an all-powerful being looms over you, loving you? Or a vast-unknown universe exists and we mean nothing. You chose. Does it matter which one is "right" if the ending is the same? You will die eventually. So either live life with hope or in fear.