The auditing guidelines stress that no internal control system however elaborate can by itself, guarantee efficient administration and the completeness and accuracy of the records nor can it be proof against fraudulent collusion, especially on the part of those holding positions of authority or trust. Internal controls depending on segregation of duties can be avoided by collusion. Authorization controls can be abused by the person in whom the authority is vested. Management is frequently in a position to override controls which it has set up itself. Whilst the competence and integrity of the personnel operating the controls may be ensured by selection and training, these qualities may alter due to pressure exerted both within and without the enterprise. Human error due to errors of judgement or interpretation to misunderstanding carelessness, fatigue or distraction may undermine the effective operation of internal control.