The writing is good and the plot interesting, but the characters' motivations remained unaddressed. I followed along, despite not knowing why this character would go there and that character would turn up here, but I felt like a small child being told to stay quiet and not ask any questions on a long and complicated journey using multiple modes of transportation. It went from being frustrating to infuriating to numbing.
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This experience made me think about the importance of motivation in a story. Why do characters do what they do? Are they confined by their personalities: a loving person cannot help but choose the loving thing and a curious person cannot help but seek out answers? Are they succumbing to circumstances? Sophie had to choose one child or the other. Are their actions solely dictated by plot?
I don't mean that we need to know at every point why a character would something. Keeping it hidden for a while keeps the readers intrigued. Keeping some motivations hidden the entire time makes the reader ponders even after the book ends. But keeping almost all the motivations hidden most of the time makes a story just a series of arbitrary events. Why would any reader care?
How much tolerance do you have for not knowing why characters do things in a book? Have you read a book that frustrated you this way?