The Kings fired Karl on April 14, one day after the franchise completed its 10th consecutive losing season (33-49). Overall, Karl went 44-68 in parts of two seasons with the Kings.
Part of Karl's downfall with the Kings was his inability to get along with Cousins.
"I never felt I got into a good place with Cuz," Karl told the Sacramento Bee in an interview at his home. "Some of that was my stupidity when I said that no player is untradeable.
"I still believe that. But I should have been smart enough not to say it, and I in no way, at any time, thought DeMarcus was going to get traded."
Karl nearly lost his job on multiple occasions during the season before general manager Vlade Divac ultimately decided to make the coaching change last month, sources told ESPN.
Karl told the Sacramento Bee that he felt a lack of support from Divac and the rest of the front office.
"Eighty percent of the time, I think the Kings did what had to be done," Karl told the newspaper. "But I'm old-school enough to think that a coach has to feel powerful, has to feel supported -- and I never felt that level of support. ... Vlade has a helluva task ahead of him. The roster needs to be tinkered with. He is going to be in for an NBA free agency unlike anything we have ever seen.
"If the decision is made to keep Cuz, you have to put the right players around him. But it can't be about Cousins. You have to make basketball decisions."
Karl, 63, praised Cousins' talent throughout the interview.
"Whether or not they trade Cuz, they have to empower their coach," Karl said. "They have to let him coach. It takes a few years to build a program. It becomes a culture, an energy force.
"Vivek (owner Vivek Ranadive) wanted magic to happen. But in the NBA, magic happens once in a while -- and usually is associated with Larry Bird, Magic Johnson or Michael Jordan. I think you can win with him (Cousins), but my thing is, how long is it going to take to get there? Then, how long before you become a winning team? I think there are faster ways to go."