Why is it of human nature to desire the ones we may not acquire?

Eyes that could not be juxtaposed with earths deep yet mesmerizing waters.
skin that could not be compared to a silkworms softest of produce. Hair that blends within the nights dark wonder and mystery.
A smile that not even the gloomiest could resist.
for she is life,
she is reason,
she is love,
she is,
Maru

Apprise me of your past, so I can understand your present and predict your future.
For I shall love you regardless.