Have you ever used the knee and guard to break an uncomfortable grip?

The hand has to go in deep, and the elbow acts in an invisible manner. The angle is important, and one of the hands does the choking while the other one just holds the collar. 

Even with all of that, why is it that the closed-guard choke often does not work out in our training sessions?

As Rickson Gracie demonstrates, it may be missing an essential resource: your legwork. 

Check out what you've been doing wrong, with yet another masterful touch.