It's not about being sure...because how can anyone be that but a major portion of the Cowboy's fanbase has seen enough of Dak and then add on how much of a cap hit he will be if Dallas gives him an extension. If the Cowboys sign Dak that means the next 4-5 years will be this huge cap figure. With Lance, if he doesnt do well then you move on after 1 year. The easy answer is Dak but can the fanbase stomach signgin him for an extension and not make a Super Bowl appearance or even a NFC championship game.
