Personality: we all have one, no matter how exciting or boring it may be.
Everyone has somewhat of an idea about the type of person they are, and can grasp an understanding of where their behaviors stem from. Understanding others' behaviors is another matter entirely. In certain situations, the ability to understand someone's behavior separate from your own seems to be impossible. Some people may find that using an idiographic (or idiosyncratic) approach to understanding a person's behavior is easier than any other approach in psychology. An idiographic approach "strives to understand personality by identifying the unique configuration of characteristics and life history experiences within a person." (Lilienfeld, Psychology: From Inquiry to Understanding)
How would an idiographic approach be used in everyday life? As a college student, you see all different types of students in a similar learning environment. Did you ever stop to wonder why there's that one student in your class that always sets the exam curve? Have you ever thought about why the student in the back of the class who sleeps through every lecture doesn't seem to care about their grades? These behaviors could be affected by the student's upbringing. The straight-A student might have parents who expect more from them than the "barely-passing" student's parents do.
Attempting to understand someone's background and personal experiences can help identify why someone behaves a certain way and may aide in learning to accept them for who they are.