Know thyself.
Prov. Be aware of your own limitations; know what you are capable of doing. (This was the motto inscribed on the temple of Apollo at Delphi.) The motto of the ballet corps was "Know thyself"; every dancer was expected to know how far she could stretch, and not hurt herself by trying to exceed her limits. "Know thyself," the high school guidance counselor admonished us, "and try to find a career that makes the most of your abilities."
Physician, heal thyself.
Prov. Do not rebuke someone for a fault or problem you have yourself. (Biblical.) Ellen: You're such a spendthrift. You should go on a strict budget. Fred: But you manage money even worse than I do! Physician, heal thyself. Jane: You look like you're gaining weight. You should probably get more exercise. Alan: Physician, heal thyself. You're getting a little pudgy, too.