This should be an
easy concept for most
people to grasp.
William Blake summed it up pretty
good with two of his
poems,
The Tyger and
The Lamb. The real
crux of these two poems is in The Tyger, the lines:
What immortal hand or eye
Could frame thy fearful symmetry?
The
fearful symmetry is the fact that both
evil and
good need each other. This is because, in defining
good, you need to reference
evil, and
vice versa. The narrator of The Tyger is a voice of
experience, though, and is therefore
tainted by the
real world. In order to fully
grasp the concept, one needs to also
read The Lamb, which will provide a
counter point.
Draw your own conclusions.