As I have noted before, Gabriella is in that "why" phase. I really try to be patient with her, as I know that she is just trying to learn about the world around her, and at four years old there is much for her to learn. However it does wear on me after about the 42nd "why", and I have to resort to one of my "shut her up" answers. (Usually "because I said so", or "I don't know". There is no fear of this child growing up thinking her mommy knows everything, because I am constantly breaking out with "I don't know"!)
This question is so ingrained into her right now that it comes out of her subconscience - literally. A true story:
The other night Bubblehead went to check on Ella before going to bed. When he went in she was sitting up, but still asleep. He watched her for a few moments and then softly put his hand on her back and said "Lay down, Baby."
Without ever opening her eyes, she replied "Why?!"
I don't know.