Marcus Aurelius · Meditations X.2
Observe what your nature requires, in so far as you are governed by nature alone. Then do it, and accept it — provided you, as a living being, are not thereby made worse.
What this means
Marcus asks what his nature genuinely requires, then does it, so long as doing so does not make him worse as a rational being. Need and integrity are checked against each other. It is a quiet test for telling real necessities apart from appetites dressed up as needs.
On nature, duty.