Even a well-designed system of internal control can break down. Personnel may misunderstand instructions, make mistakes in judgment, or commit errors due to carelessness, distraction, or being asked to focus on too many tasks. For example, a department supervisor responsible for investigating exceptions might simply forget or fail to pursue the investigation far enough to be able to make appropriate corrections. Temporary personnel conducting controls for vacationing or sick employees might not perform correctly. Changes in information technology application controls may be implemented before personnel have been trained to recognize indicators that they may not be functioning as designed.