You see it all the time on a game shows like "Cash Cab", or "Deal or no Deal". The contestants chooses between walking away with a substantial amounts of money, or betting it all on hopes of hitting the jackpot. Clouded by greed and the excitement of the show, contestants go for the jackpot and lose.
In casinos, gamblers on a hot streaks also rarely stop to leave with their winnings. Instead they give in to temptation and continue playing. Soon all of the winnings are gone.
The rational decision is to humbly accept good fortune for what it is, and to not sacrifice windfalls in the name of greed. So, the next time you find yourself in this situation remember just take the sure money and walk away. I guarantee its better than nothing.