Having to choose between the human faults of Envy and Greed, most of us would instinctively reject both as negative traits - and we've all grown on numerous stories and metaphors explaining why we should avoid either one of them.
But a while ago, reading For the Win, by Cory Doctorow (highly recommended book, highly recommended author) I ran into a paragraph (regarding economics of gaming) that boiled down to the following:
Greed is about wanting to have what others have and you think has value. Envy is about wanting to have what others have and others think has value.
And this made me realize that yet again, "forces of evil" (Greed and Envy in this case) can be used for good.
You can use Greed - to see how others are - and wish to be like them.
You can use Envy - to see how others wish to be - and learn what to wish for.
Get it! Got it? Good...