"It is important to remember, in this context, that for Epicureans all virtues—like moderation and justice—are defined not absolutely, by an independent objective standard. They are instrumentally valuable because they contribute to a pleasurable life, and so what counts as virtuous in a case depends on what in fact produces happiness (Ep. Men. 132)."
Definitely a paper I want to read. That simple statement has profound implications, and I think is very difficult to appreciate without working on a drastic overhaul of the way we think. The same action that we normally see as courageous becomes in fact foolhardy in the wrong circumstances. The action isn't just "courageous, but sadly turned out wrong" but in fact no longer meets the definition of courageous in the first place.
At least in my mind that is very hard to appreciate. My mind wants to say courage is courage is courage and place the blame for a bad result somewhere else (luck? fate? gods?) rather than think that courage has no set definition that applies at all times and places.
But that seems to be exactly what Epicurus is saying, and he hammers it home apparently in his own words in those statements about "justice" at the end of the PDs.