Earlier in the game when faced with a Daily Double, Cooper made a huge risk and wagered $18,000. The audience gasped, but Cooper surprised them all with the correct answer that doubled his earnings to $36,000. This put him in the lead amongst the 2 other contestants, and Cooper well knew that the person with the highest earnings would get a minimal of $75,000. So, when faced with the Final Jeopardy! clue, "On June 6, 1944, He said, 'The eyes of the world are upon you,'" Leonard cleverly wagered $0 and responded: "Who is some guy in Normandy, but I just won $75,000!"
Here's the punchline: One of Cooper's opponents had enough earnings to surpass him if he answered correctly, but he didn't, and so Cooper won the tournament and went home with $75K. Even host Alex Trebek was excited by Leonard's confidence. He laughed and said, "You did indeed! Way to go!"
