A high risk / high reward operation. The phrase originates from craps where a hard
six is achieved by rolling threes on a pair of
six-sided dice (3+3). Rolling a hard
six has a probability of about 3% whereas rolling six by any other combination has about a 14% chance. A hard six pays
7 to
1 whereas a regular six pays only 7 to 6.
The phrase was used by the character Commander/Admiral William Adama in the television series Battlestar Galactica.
Dude: You should ask her out!
Guy: But what if she turns me down?
Dude: Sometimes you just gotta roll the hard
six.