How do you win a reality contest? Start off well (but not great), improve with time until the end, when you blow them out of the water. Usually, it's those people who show improvements at the end who win it all, and the ones who start off big inevitably can't sustain it and end up falling short.
I submit Evidence A: Kelly Clarkson, American Idol 1
No one knew who she was when the semifinals started. She was never even shown once prior to belting out Respect in that semifinal round. She began to make a name for herself with that performance but didn't step out from behind Justin Guarini and Tamyra Gray's shadow until the Top 6 show with her brilliant "Stuff Like That There" performance. While Justin and Tamyra showed flashes of both brilliance and what-the-hell-were-you-thinking performances, Kelly was building a juggernaut, and nothing could stop her victory in the end.
Evidence B: Kelly Monaco and Drew Lachey, Dancing With The Stars
In season 1, Kelly Monaco nearly got kicked out the first week, but she kept improving week after week (she couldn't have possibly gotten worse; she was pretty awful to begin with), and her improvements endeared her to judges and voters, and she beat early favorite John O'Hurley in the finals. Of course, it didn't help that John had an ill-advised freestyle dance. I wouldn't say that Drew Lachey improved since he was good from the start, but he smoked it in the end, while judges' favorite Stacy Keibler played it safe towards the end and maintained status quo or regressed.
Evidence C: Kristy Swanson/Lloyd Eisler, Skating With Celebrities
Finding romance off the ice (coughHomeWreckercough) has certainly helped this pair in regards to chemistry and showmanship, but what also helped them was a slow start to the show. They were nearly eliminated in the first round but kept getting better and better. Meanwhile, the show's ringer, Jillian Barberie, and her partner John Zimmerman, looked like a professional pairs team in their first performance, and they had nowhere to go but down. They have more or less phoned it in each week since. Monday's performance was better artistically than most of the stuff they'd done since week one, but they had a really big blunder when John nearly dropped Jillian on her head during a lift. The pairs still have one more skate left, but unless Kristy and Lloyd bomb and he drops her through the ice, look for a Kristy/Lloyd "comeback" victory.