I would alter that slightly: virtuous acts should be done whenever an opportunity arises. When we see particularly conspicuous acts of virtue, by which the practitioner benefits greatly, especially when the opportunity to avoid conspicuousness existed but was eschewed, we are right to suspect that the act would not have taken place in the absence of an audience, and thus actually signals a lack of virtue. (Because the virtuous act so regardless of audience, and personal benefit, and even at great personal risk or hardship).