I'll repost part of something from the "What's Wrong With Her?" thread:
Adding to that, as the post-Wimbledon victory years pass, Kvitova does not appear to posess a natural champion's mentality--the instinct and vision to see majors as something they deserve to win, rather than hope to win. The differences are absolutely critical, as the former removes most doubt and confusion, and allows the player to see the opponent as someone that is merely "a fight on their way to the title," as opposed to the latter, which leads the player into believing oppenents are "someone I might have a shot against."
As of this date, Kvitova had the former for exactly one moment in time. I still think she's on the path to being a one-major wonder, but I give her a small window for serious retraining of her mind and body to be able to forcefully use the skill which won that lone major.
She's not in the washout zone occupied by Wozniacki, Safina or Jankovic, and she has more natural talent than here-one-year-gone-another majors winner like Kuznetsova, but she is wasting her best years being introverted, and lacking every ounce of that deserve to win vision & instinct.