Duke has already beaten Kentucky, Louisville, Ohio State and a pretty good Temple team this season, but the Blue Devils' long-term success comes down to one player.
He's the straw the stirs the drink. Without him, the team is rudderless.
Cook has improved in his second season, but he's still erratic at times. The sophomore is averaging nearly 11 points per game and just under six assists, but he still makes critical mistakes at times, and that's tough to stomach for the team's point guard.
For all of his early success, Cook is still turning the ball over nearly three times per game. He's shooting less than 46 percent from the floor, and he picks up nearly three fouls per game because he hasn't learned to play aggressive, and smart, at the same time on defense.
This isn't a question of talent. There's very little doubt as to how good Cook can be. He just needs to slow down sometimes. He gives the Blue Devils an element of quickness that no other player can give them, unless you count Tyler Thornton's presence off the bench.
Duke needs Cook to grow up in a hurry, and he already has. Seth Curry is much better off the ball, and so is freshman guard Rasheed Sulaimon, who is already showing that losing Austin Rivers to the NBA was addition by subtraction.
This team has it figured out. Along with those guards, Mason Plumlee is dominating on both ends of the floor, and Ryan Kelly continues to be an extremely difficult matchup for opposing defenses. Together, the two big men form one of the nation's most dangerous high-low combinations.
Cook is the team's ultimate X-factor. When he's on, he's a whirling dervish of activity, slicing his way to the rim and drawing a foul or pulling up for a long-range shot. He's also exciting on the defensive end, which is why he's averaging just over 1.5 steals per game.
However, Cook can be just as frustrating as he is exciting when he's off his game. He tends to go a bit too fast for himself at times, causing mistakes and messing with the team's rhythm. It also throws his shooting out of whack.
This idea all came to a head versus Temple on Saturday. Cook played 14 points, dished four assists, had three steals and only turned the ball over twice in 36 minutes.
He controlled the tempo of the game like no other Duke player could, and the Blue Devil could have, and the team dominated the Owls for two straight halves.
If Cook brings his best game consistently, the Blue Devils are going to be very tough to beat all season long.
They have every element that a championship team needs. Now, they just need Cook to steer the ship.