"Look me in the eyes . . . ."

... And tell me the truth, or tell me you do or don't love me. Those are the usual endings to that sentence. People use it all the time in movies and books, most often in regards to love. Someone will tell the person they love to look them in the eyes and say they don't love them back. Inevitably they will be told no, for reasons of great noble sacrifice, sometimes. More often than not the 'no' comes from fear. Regardless, why do they keep asking "look me in the eyes . . ." and expect to have some magical ability to know the truth? Or, every time they believe what they are told, also probably out of fear, that their 'worst fear' is coming true. I am fascinated by this. Apparently I need to work on my ability to read eyes in order to better understand why it is used so much.