Who you think you are, is the person who you will present to others. Some people choose to be like that or because of certain upsetting/traumatic experiences, people think of themselves lower than who they really are.
Upsetting or traumatic experiences may originate as soon as soon as after you were born and right through your lifespan. Experiences like being discriminated upon by significant persons, like your parents, siblings, people you esteem for their authority etc. Examples of this can range from not regarded to abuse. Like on everybody else’s birthdays there will be family members wishing them a “happy birthday” and presenting a gift, but when its your birthday nobody acknowledges you. Everybody else get gifts but you. Your siblings can sit on dad’s lap, but you cannot. Everybody else is acknowledged at the dinner table but you. All the other siblings get the love they want from their parents, but you. To be told that your parents did not want you to be born, and been called a “misfit” or “ugly.” How can you feel any self-worth if you were discarded at an orphanage and your own parents rejected you? “Scorn has broken my heart and has left me helpless; I looked for sympathy, but there was none, for comforters, but I found none.” (Psalm 69:20)
Repeated rejection and discrimination is the fertile ground for low self-worth. When you crave that love and affection you so deeply wanted and never got, it may affect the way you see yourself. Though this may be you, you can find comfort to know this truth, “The Lord does not look at the things man looks at. Man looks at the outward appearance, but the Lord looks at the heart.” (1 Samuel 16:7)