When you're audited, have fun claiming you didn't know that you were committing tax evasion.
Try buying something for a ridiculously low price down the pub. When the police come to take the stolen goods away, try claiming you didn't realise something selling for a tenth of its value was stolen.
Knowledge of the act, not knowledge of the law. There are very few contexts in which you can be punished for not knowing an illegal act took place, and they are all situations where you should have known but were negligent.
>'When troops commit massacres and atrocities against the civilian population of occupied territory or against prisoners of war, the responsibility may rest not only with the actual perpetrators but also with the commander. Such a responsibility arises directly when the acts in question have been committed in pursuance of an order of the commander concerned. The commander is also responsible if he has actual knowledge, or should have knowledge, through reports received by h'un or through other means, that troops or other persons subject to his control are about to commit or have committed a war crime and he fails to take the necessary and reasonable steps to insure compliance with the law of war or to punish violators thereof.'