just like with the moon and wolf, the moon loved the sun enough to give half his life to her, but smart enough to keep the other half, in case she decides to break it,
the reason we have night and day, is because the moon loved sun, but sun wasn't blinded by her light to see it, but blinded by his appearance to embrace it
really, i always believed the real reason we have night and day is because the moon loves the sun but the sun doesn't love them back.