"I can't wait to contribute, I can't wait to play this game and just prove people wrong," Jack told The Rich Eisen Show on Monday.
He'll get every chance to do so beginning Thursday, when the Jaguars open rookie minicamp, and said he'll do so with no limitations from a right knee injury that ended his final college season prematurely in September.
"It's all motivation and I actually appreciate it. It's made me hungry. It's grounded me a lot," Jack said.
He had hoped to be chosen by the Jaguars all along, but the No. 5 overall pick was the slot he had in mind. Instead, due to NFL teams' concerns about the longevity of his career and the possibility of more knee surgery in the future, he fell out of the first round entirely. Jack told Eisen he and his family watched the second day of the draft from a Chicago hotel rather than returning to the green room Friday with other invited prospects who were not taken in the first round.
"It was, honestly, humiliating. It was embarrassing having to sit there, and afterwards walking out, having my girl to my left, my mom to my right, my grandmother to the right of her and having to look at them, it was a tough feeling," Jack said. "It wasn't a good night, truthfully."
The former UCLA star, who played part-time on offense early in his college career, said his two-way ability was nearly a topic during his pre-draft visit with the Jaguars.
"When I went down there the running back coach tried to pull me aside, but the linebacker coach wasn't going for it," Jack said.
Nor should he.
The Jaguars' defense ranked No. 24 in the NFL last year at 375 yards allowed per game, and Jack is determined to show his knee won't prevent him from giving that unit a boost.