First of all if you decided to watch this movie based on seeing the poster or the trailer you need to be aware it is not as hilarious as you thought. Also, if you are feeling bored or down please watch other movies that has more actions and thrills, as this movie is mostly about the dialogues between Jae Hyun and Soo Jung, the main leads, no antagonist involved. That's the reason why some comments and reviews stated the movie is boring. But their conversation is actually pretty deep and meaningful while they share and exchange their values of love and sex in a mature way. Mature because there is no slapping, kabedon (wall slamming), force kissing, stalking, piggy back riding, or any other cliche you may find in typical rom-coms. Actually most funny scenes come from the poor friend who is kept left behind by the jerk, that I think are just fillers to make this movie looks funnier.
The aim of this movie is actually the thought process of digesting shocking ideas unfamiliar to the leads: for Soo Jung is finding her first love marries a girl only after 2 months of dating and a stranger asks her straightforwardly but earnestly for a one night stand; and for Jae Hyun is meeting a beautiful woman with a 10 year steady relationship and a basketball player who disregards promising future for a girl.
Some criticizing about the cheating idea is made permissible through this movie. But in my opinion not in this movie. Fate is definitely plays a part as Jae Hyun said in the beginning, although Soo Jung disagrees but you will agree with him after finishing this movie. Soo Jung 10 year relationship with her boyfriend is just exist, something to make a late 20's woman feel comfortable and secure without any excitement (she can't name any fun she did with her boyfriend when Jae Hyun asks).
This kind of movie needs two main leads that can deliver strong chemistry, and the couple nailed it. Yoo Yeon Seok was charmingly seductive yet earnest and Moon Chae Won was naturally uncomfortable yet determined made Jae Hyun and Soo Jung's one day life change event believable. They acted out deep conversation and facial expressions very well.
The OST songs "Photograph" and "Kiss Me" by Ed Sheeran are romantic and soothing.
Since this is a nice romantic movie not drama, definitely the rewatch value is high, though you may not want to rewatch it if you want scenes with lots of actions. But if you feel stuck, watch this film it will make you think of a new idea or rethink about an old idea to be changed.