First things first I was bored the first half of the movie, nothing really happens since they're setting what's about to happen. I usually like slow paced movies but this was definitely not one of them, at least for me.

Plot: This story follows Mi Ju, a teacher at a conservatory (I suppose), we find that she is a teacher of cello hence the title of the movie.
Like I said the first half of the movie there isn't much happening besides finding out that she has a daughter with a disability and she blames herself for that and takes some type of antidepressant pills.
Later one people start dying and we make the connection that that is a ghost hunting her due to a past event in both their lifes. Now here it starts my problem, Mi Ju tells her husband the story about how she used to be best friends with our ghost and that she used to be jealous because she was the best and the ghost always felt that she lived in her shadow. After a recording they both find out that Mi Ju was the selcted one and they have a car accident in which ghost friend dies. Mi Ju blames herself for that and believes that's the reason why all this is happening, even though she wasn't even driving but still.
Later on after her younger child is dead, aunt is dead, husband is dead the only one left is her oldest daughter, Yoon Jin.
She finds Yoon Jin playing the cello which she grabs and destroys with a golf club but not really because she was trippin' all this time and the cello was actually Yoon Jin and she killed her.... but not really. Plot twist! We get back to the beginning of the movie where Mi Ju has suffered a car accident and is being taken to the hospital and she is ALIVE and wakes up and it was all a dream!! Ugh... but not really, again, because (this is my interpretation on the movie, yours might be different) she's stuck in a sort of groundhog day and everything will repeat again.

Now hear me out, I liked the 1st plot twist which it was the story she told her husband about ghost buddy being jealous and all that, but in fact being actually the opposite. Mi Ju was the one that lived in the shadow of her best friend, her friend was the one that was choosen at the recording studio, etc. Also the car accident, Mi Ju was driving, they have the accident and ghost friend is holding on for dear life asking Mi Ju to save her and what does our lead do? She lets go of the hand of ghost buddy, she falls to her death and yes that, technically, makes our lead a murder because she thought if her friend died she would be choosen and everyone would finally pay attention to her and see how great she is. So now at this point I'm sympathizing with the ghost more than Mi Ju, I actually really liked this twist but then they do the whole this was a dream, and I was just like "......Really....?"
And afterall it wasn't a dream and she was stuck living this day forever or not, I don't know.
I just feel like it was really pointless and wish they had ended the movie when Mi Ju killed Yoon Jin.

Acting/Cast: It was kinda meh, my favourite scenes were the ones with the kids aunt and Yoon Hye, That kid was the cutest.

Music: It's mostly classical music mixed with some eerie, synth music. So it was okay and didn't bother me.

Rewatch: It's not really worth rewatching it.

Overall: It had it's good points but way too many plot twist's which made me lose interest in what was happening besides the movie totally didn't go where I wanted it to go.