The Generation of The Flood. More specifically, the generation of the flood in Genesis 6. Commentaries pinpoint their tragic flaw as gezel v'genef, or petty theft. They were said to be stealing the equivalent of half pennies from each other, eventually eroding trust and pulling down the civilization into a state of moral topor (perhaps a prelude to Sodom and Gomorrah?). The opposite of this flaw can be seen in the generation of the Tower of Babel.