I find that the best virtue I have has in it some tincture of vice.

Your best qualities are not pure. Generosity carries some wish to be seen giving, patience carries some avoidance, courage carries some appetite for risk. Knowing this is not a reason to think less of the virtue; it is a reason to stop being shocked when the mixture shows.

Take the quality you are most sure of in yourself and look for the small self-interest riding alongside it. Not to condemn it, only to see where it might tip. Someone who knows which way their virtue leans is harder to catch out than someone who believes it is clean.