The biggest problem that we face in jiu jitsu when attacking the kimura is simply moving the hand from the front to the back. While this may seem simple in nature, there are a lot of components to this.
According the John Danaher, the kimura grip is not only a strong powerful submission, but it is also a very empowering restraining tool. This is why the kimura is considered on of the most versatile weapons, and why John Danaher has a whole series on how to attack the with the kimura.
One of the best aspects about the kimura attack, is that it also opens up other opportunities to chain the kimura to other submissions.