em Jeopardy! /em 's Most Infamous Moment Haunted the Show's Fans, Its Stars, and Even Alex Trebek. It's Clear Why Now.

's most controversial moment was years in the making. It took many more for the fallout to come into full view. One morning in 2010, Alex Trebek walked onto the IBM campus not far outside New York City and prepared to inspect what would become the most unusual player in's history. The trip, clear across the country from the show's Culver City set, had been carefully planned. David Ferrucci, a computer scientist at IBM, had spent years leading a team to develop what would become the first and, so far, last nonhuman ever to compete on Longtime host Trebek would watch three practice games played with "Watson," as the system was named, and two human contestants. Then the team would be taken to lunch nearby, and Trebek would ultimately take the stage and host two more Watson practice games himself. By then the preparations for a future televised contest with IBM's creation were well underway, but this was the first time Trebek would encounter the technology in person, and his approval was crucial. Ferrucci was eager to show off one element in particular: the display, which had been rigged to show Watson's top three guesses whenever it answered, along with the numerical confidence rate it had in each one. For Ferrucci, this feature was central to demonstrating the computer's language-processing capabilities, because it showed that Watson wasn't just spitting out answers--it was reasoning. If Watson were ever going to be deployed to industries like health care, its human users wouldn't just want to know its best guess. It would be infinitely more valuable to know if Watson was 95 percent confident or just 30 percent, and whether those confidence levels were in line with its actual accuracy rate. It also made for better viewing. Ferrucci had brought his young daughter to the lab earlier in the process and showed her Watson as it played against human opponents. When Watson declined to ring in, Ferrucci's daughter turned to him and asked if the computer had crashed. He struggled to explain that it hadn't--it just wasn't confident enough to hazard a guess.