What is Mark Cuban's biggest regret?

It has nothing to do with the circumstances of a big game or his relationships with his past coaches or lambasting commissioner David Stern or losing out on a key player.

Give up?

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"Letting Don Kalkstein, our psych doctor go," Cuban said Tuesday during an appearance on ESPN Dallas 103.3 FM's Ben & Skin Show.

Co-host Jeff "Skin" Wade, an admitted unabashed Mavs fan, instantly responded by saying, "C'mon, really?"

"Seriously," Cuban said. "I think if I hadn’t done that we win a championship with Avery (Johnson)."

It was Johnson, who holds a psychology degree from Southern University, who no longer wanted Kalkstein around. Cuban listened to the young head coach he promoted in 2005 and made it so. Kalkstein then joined the Boston Red Sox and wears a 2007 World Series ring. He rejoined the Mavs as director of sport psychology after Johnson was fired in 2008 and Rick Carlisle was hired.

The Mavs, one might remember, from Cuban to Johnson and all the way down, melted into a puddle of goo in Miami during the 2006 Finals. Johnson panicked and moved the team from the party scene in South Beach to placid Fort Lauderdale, a tactic that failed to prevent the horrific collapse that saw Dallas' 2-0 lead over the Heat disintegrate into a six-game defeat.

Kalkstein, now well into his second stint with the Mavs -- as well as the Texas Rangers -- might have helped blow all that steam in a more productive direction.

Cuban was fined $250,000 during the '06 Finals for repeated misconduct, Johnson lost his cool with a reporter after a loss in Miami and the franchise suffered the ignominy of being called chokers -- a moniker that would stick all the way up to the 2011 triumph. Kalkstein is heaped with praise for his work with that team, one that emerged as stunning mental heavyweights.

"Organizations may not win championships, but organizations can lose championships," Cuban said. "I think there’s just so many little things that people don’t realize are important. That’s why you hear terms 'coach killers' and you hear about dissension in the locker room. All these little elements are critical. We’ve had years where we’ve had great teams and my inability to solve that problem or in the case of not having Doc there, hurt us, so literally that was the biggest mistake I made."