Okay first off this movie was so bad and i'll explain way.
The ML liked the FL but it wasn't explained why at all. He didn't show he liked her at all until some time later in the movie.
It also wasn't clear why the FL liked the ML and when she even developed those feelings...

The movie starts off with the ML being an unfriendly asshole, yelling at the FL for no reason. The FL is a winy girl who has never dated before because of unknown reasons. She then gets that book which just is like that magic shell from SpongeBob kinda telling her what to do and so she starts to act according to the book.
The ML asks her to date him out of nowhere and it is them revealed he likes her and he claims he had given her so many hints. However he keeps pushing her to give him an answer in a very unfriendly way, even calling her names. He doesn't respect her boundaries at all.
His twin sister is also meddling in all this and calls her a tomboy for the simple fact that she isn't wearing skirts put pants. What kind of message is that?

The FL struggles with her private life as her Mom has Alzheimer and obviously that's a lot to take care of. However her Mom is not very much discussed until she appears at FLs work place with no shoes and stinks for some unknown reason. FL is embarrassed and doesn't let ML help her get her Mom home. In her own words, her pride didn't let her.

The ML and his twin sister also try to push the FL into accepting a bakery school something in Japan. The twin sister first pressures her by telling her the ML would basically miss out on an opportunity because he was scared the FL would get a bf in the meantime. Which is kinda emotional blackmailing? Like why would you put that on her? If he is dumb enough to mess with his future because of a girl who doesn't seem interested in him, then so be it??

I feel like the twin sister and ML don't respect the FL and treat her as a child that is incapable of making her own choices. They also don't want to respect the fact that she doesn't want to leave to Japan and keep asking her about it although she doesn't owe them any explanation.

Also the ML is like "I would be very close blabla" basically implying they would go to Japan together for 6 months although the FL didn't even respond to his confession which wasn't even a confession. He doesn't even say he likes her to her face.

FL totally freaks when she looses the book because she in fact actually is incapable of making her own decisions and was relying on the book to tell her what to do. This isn't seen as problematic tho. You will know at the end why.
The FL was very very unlikable. She wasn't nice, she wasn't caring, she was always lost in thought, once setting the kitchen on fire, endangering everyone and almost set it on fire for a second time because she kept forgetting things in the oven or stove. This eventually leads to her ruining a cake which was pre ordered. I am sorry but I would fire her or at least tell her off because she can't be this dumb at work. But the ML instead just steps up for her and takes the blame and now it's her turn to be super disrespectful...dude he is your boss what are u thinking talking like that to your boss and questioning his authority.
And on top of that she confesses that she likes him but instead of this being a romantic moment where they finally end up together, it results in him leaving the cafe because she can't be around him?? it's his cafe, why would you leave? At least he takes on the job in Japan for a few months but he just lets her stay and he didn't even confess that very moment when she said she liked him...which I want to ask again...when did she start liking him and why?

The movie ends with her finding a book again. Turns out ML had a book made that looks like that but with empty pages.
It was revealed he apparently liked the FL for a very long time and even kept her picture in his car.
FL hands in her resignation letter after finding out he had the picture which I didn't understand at all..because she then opens the just found book where the ML glued a picture of her saying he loves her which makes her go to him and suddenly he picks her up and spins her around?
Please what is this...

Sung Hoon was his typical self drama character. Unfriendly seemingly cold prick with a soft inside.. FL was just unlikable from beginning to end and didn't make sense at all. It didn't make sense why she avoided him eventho he liked her and she liked him? What is the reason? Somebody tell me.. Yes there was the mother illness thing but it doesn't add up and she was actually desperately looking to fall in love and find a boyfriend and when there is literally her chance she just walks away? Also she did only act according to the book to find a boyfriend so what was the point of everything and what was the point of freaking out when the book disappeared when she wasn't even interested in pursuing a relationship with her boss/the ML.

So yea to sum this up, acting was normal but the story was horrible. Whoever had this idea...just don't make this into a movie...It wasn't romantic, it was more of an dependency and very unhealthy relationship that didn't make sense whatsoever because both characters were pretty much unlikable, had almost no good traits to them, there was no spark, no tension, no typical scenes with accidental skin ship nothing. The movie was blunt, the characters moody and cold..the side characters were overall unnecessary and didn't do anything for the movie. Character development was pretty much non existent, other than the FL who got more and more unrelatable and annoying and whose actions kept making less and less sense.