the body of my enemy

As an old saying (Chinese? Japanese?) has it more or less: "If you watch the river long enough, you will see the body of your enemy float by."

Somehow this dovetails in my mind with, "Do not be too virtuous. Too much virtue makes people crazy." (Provenance likewise uncertain, but nonetheless stuck in my mind.)

How long can the seriously-committed be good before all that's left is what was once dog-tagged as evil or naughty or not-to-be-done? How long can the seriously-committed be evil before all that's left is what was once dog-tagged as good or pure or to-be-done? Yes, I can hear the natterings in the rafters -- purity/clarity/understanding are endless, right? -- but I still think the body of anyone's enemy is bound to float by.

Seems like "square one" is always the only option.