When a reader takes on the struggles and emotions of a character in a work of fiction, what is this called?
When a reader really starts to react to a book and feel as if they relate to the characters, they are identifying with them. Identification means that the reader sees something in this fictional character which could resemble themselves and their personality or the surroundings they are living in. Readers can even feel like the struggles the character goes through mirrors their own, and so connect on a deeper level with the book.
Rich imagery and vivid symbolism are key to helping the reader experience this, and indeed it is the ultimate aim of the author to capture the readers attention and imagination so fiercely that they feel like they are a part of the book. That is the true aim of reading.