Sometimes we get to involved with one part and forget the rest. For example if you roll with your hands cuffed behind your back and you move your shoulder preparing for the roll you may forget the neck and the rest of you and get bumped or more. Remember to be aware of all your parts and than you will be able to use them. Another example is when you are being chocked on the ground or standing up and many start to strugle with the upper body forgeting their legs frozen. You have to be aware of yourself to move properly. You have to study this well.