Suffice to say that you cannot fire a decent score with any gun at any range if you continually change your grip or position. Jerk or Heel. The application of pressure either with the trigger finger alone or in case of the heel, pushing with the heel of the hand at the same time. Apply pressure to the trigger straight to the rear and wait for the shot to break. Anticipation can cause muscular reflexes of an instant nature that so closely coincide with recoil that extreme difficulty is experienced in making an accurate call.
Anticipation is also the sire to flinching.
Loss of Concentration. If the shooter fails in his determination to apply positive pressure on the trigger while concentrating on the front sight his prior determination needs renewal and he should rest and start over. You work and work on a shot, meanwhile building up in your mind doubt about the shot being good. This is a mental fault more than a physical one, which results in your accepting minor imperfections in your performance which you could correct if you worked a little harder. The end result being you hope you get a good shot.