Question: [Source](http://www.imdb.com/title/tt1371111/synopsis?ref_=tt_stry_pl)

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> she meets a man named Hae-Joo Im, who it is revealed was behind her friend, and then her.
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What does this mean behind her friend, and then her?

Answer: 
I like to think of it as the difference between "weather" and "climate".

Weather is what's going on right now. Being "cheerful" means that, right now, you're upbeat and feeling good. - Like if the weather is sunny.

Climate is what the overall weather is like for a region. While it may be sunny today, if the general climate is for cold, damp weather, the sunny day is unusual. Same with being happy. In this case, he's using happy to mean that he's not sure he's generally happy with his life but, for the time being, he's cheerful.
Be cheerful no matter what happens...