That may apply to shoplifting, but not when you're predicting your behaviour in different situations - "I would be good even if given more power".

From Why Does Power Corrupt?:

The young revolutionary's belief is honest. There will be no betraying catch in his throat, as he explains why the tribe is doomed at the hands of the old and corrupt, unless he is given power to set things right. Not even subconsciously does he think, "And then, once I obtain power, I will strangely begin to resemble that old corrupt guard, abusing my power to increase my inclusive genetic fitness."