This little book I'm reading (The Greatest Miracle in the World) mentions how Alexander the Great handled a situation like this:
"It seems that the great general was about to lead his army against a powerful foe whose men greatly outnumbered his own. Because of the odds against them, his army had shown little enthusiasm for the upcoming battle as they set sail for what they feared would be their end. When Alexander finally unloaded his men and equipment on enemy shores he issued an order for all his ships to be burned. As their means of retreat slowly sank in flames behind them Alexander rose to address his men and said, 'see your crafts going up in smoke, their ashes floating on the sea? That is our assurance that we shall be victorious for none of us can leave this despicable land unless we are victorious in battle. Men, when we go home we are going home in their ships!'"
I'm sorry, but that's just badass.