A Fly once bit a Bald-man's head.
Thinking to strike the creature dead,
He gave himself a painful blow,
And let the little culprit go.
The Fly went laughing off, and cried,
"The stroke, good Sir, was well applied;
Had you not death design'd for me,
Less painful now your bruise would be."
"The pain I've given myself," replies
The Man, "I readily despise,
Because it was against my will;
But those whose nature prompts to ill,
Who live by sucking others' blood,
I would extirpate if I could."
By fate or sudden impulse driv'n,
Who reckless sins, may be forgiv'n;
On who deliberately does ill,
Her utmost let the law fulfil.
Source: Boothby - Phaedrus 5.3.