Who wants to read a story that starts with the birth of the main character and follows them through their entire life? This method of fiction writing is hardly ever successful. Why? Because readers will not care about everything that happened to the character when he was two, three, four, and more. They want to get to the action… the stuff that matters to the story or book in front of them.
But what about backstory? Information that happened outside the scope of the piece of fiction writing is often necessary to understand the plot. A character’s history can provided needed clues about their current emotional state, goals, or reactions to events. Some backstory must be included.