It's the mental fortitude that has been lacking, according to Cardinals coach Bruce Arians.
"Talent [is] not an issue," Arians said Wednesday. "Maturity is. And it's just maturing."
This is the second straight season the Cardinals have had maturity issues with their first-round draft choice.
On Nov. 8, Arians said the adjustments to being a professional that Nkemdiche had been experiencing were "very similar" to what Humphries went through last season.
But on Wednesday, Arians said he can't compare Nkemdiche to Humphries anymore. "No, D.J. worked harder," Arians said.
One of Nkemdiche's most recent incidents that magnified his immaturity came after Sunday's loss to the Minnesota Vikings in Minneapolis.
He was wearing a T-shirt under his suit, instead of a buttoned-down shirt and tie -- the standard dress code for a trip home after a road loss -- and Arians reportedly had a few choice words for the rookie about his outfit. Nkemdiche proceeded to find a tie but had to ask a teammate to tie it for him, then he wore it over a T-shirt. He reportedly later was given a dress shirt to meet the team's dress code.
Nkemdiche's issues this season began the week before training camp, when an ankle sprain sidelined him for most of training camp. And they have just continued.
In mid-October, Arians graded Nkemdiche's season as a "C." He criticized Nkemdiche for being "overaggressive."
"You don't have to be Superman just because you're a first-round pick," Arians said then. "You don't have to go out there and get all crazy and get out of your gap. Just do your job."
In early November, Arians said Nkemdiche was still learning "the sense of urgency at this level," citing Nkemdiche's actions in meetings, the weight room, on the field and with assignments.
"He just needs a little more of a sense of urgency," Arians said.