Watching Wheel of Fortune at home and actually playing it in the show are two very, very different experiences. It's easy enough to know the answer on your couch, but it doesn't always come to you at the moment when you are on the show.
Of course, sometimes you might just not know a certain word or phrase, or might think it's spelled differently than it actually is. Either way, it can be embarrassing to get wrong. Which, unfortunately, is what happened to one Wheel contestant last week.