Why do we say the apple of someones eye?

Apples are good but come on now they arent that great to look at! If i am forced to look at a piece of fruit then i think i’d want to look at something more interesting like a… oh i dont know a… pineapple. then again, the word pineapple has the word apple in it too. so maybe i’d look at something like a kamquat! yeah thats it! kamquats seem like a fruit that could occupy a lot of someone’s time. Dont you? But i think that comparing someone or something you love, like or admire seems dumb to me? Ah oh well.

Why DO we say the apple of someones eye?