Have you ever assumed you have been attacked, only to have the person you thought was attacking you say they are not attacking you?
When attacked, people defend themselves. So if you were not actually attacked, but thought you were and acted to defend, then wouldn't that defense become an attack?
If you did attack someone and they defended, then you told said person you hadn't attacked, wouldn't that be a kind of defense against the defensiveness caused by you the attacker?
Umkay, time for ibuprofen.