This question has many answers. We think in terms of our feelings, our looks, status or abilities, just to name a few. I feel experiences and conditioning play a large part in how we view ourselves. Maybe insecurity or emotional pain is some of what causes one to even ask this question. A sense of low self worth. Even if these reasons do not fit everyone, there may come a time in later life when a small doubt arises that makes one wonder if, "this is all there is" or "have I made a difference in anything?" Personally I feel that we compare ourselves too much with others or with what society in general expects, therefore we lose that individuality we were born with and become clones. Take a long look in the mirror, stand there and ask yourself the question: "who am I?" Try this.