The apple of your eye is that person (or thing) that you care for the most. Example: "He sure does love his little girl." Reply: "She's the apple of his eye." Example: "You got me the bracelet I wanted!" Reply: "Yes, I knew it was the apple of your eye."

The original meaning of the apple of your eye is the pupil, or the round black spot in the middle of the eye. It is as if that person's reflection can be seen in the pupil ("apple") of your eye. Example: "Everyone knew they would get married someday. She was always the apple of his eye."

It makes you feel good to look at the person who is the apple of your eye. From a famous love song: "You are the apple of my eye. That's why I'll always be with you."