In *The Force Awakens*, we learn in the opening crawl that Luke Skywalker has disappeared.

He is in fact 

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>  absent for most of the movie except for a few seconds at the very end (and in a vision / flashback scene). 
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Why was this? 

I am looking both in *and* out-of-universe explanations.

**1. In-universe:** Why did this character disappear, choosing to essentially go into hiding?

**2. Out-of-universe:** Why did the filmmakers choose to 

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>  leave this Luke Skywalker out of the main story?  
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> (i.e. Did Abrams think Mark Hammill was a bad actor? Was he busy or sick? Anything like that...)
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