What does "reign it in" mean?
What does "reign it in" mean in below context?
The Stephen you know was a "good behavior" Stephen, "reign it in" Stephen, "fight against his nature to an annoyingly absessive level" Stephen.

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Answer

It's the wrong word, even though the pronunciation is exactly the same. The phrase is "rein it in".

Reins are the straps which are used when controlling a horse. ("Reign" means to be the monarch of a country.)

http://idioms.thefreedictionary.com/rein+in

Answer

I haven't heard of "reign" being used like that, but it seems like it may have been mixed up with "rein in" as an expression of "withholding/controlling emotion" that originates from pulling back the reins of a horse to stop/control them.