What does knowing a motivation help the reader better understand?

A character's motivation is the driving force behind that individual's thoughts and interactions with people around them. Understanding what it is a character want helps a reader grasp what is at stake on that protagonist/antagonist journey they're experiencing throughout the piece of writing; in addition, a well crafted goal provides readers an opportunity see inside someone they either identify with or perhaps feel a great distance from because of differing life choices or priorities in life.