I stopped trying to understand my daughter and her addiction, when I accepted her and accepted being powerless over her. I'm not sure when it happened but, somewhere along the line, acceptance became more important than understanding, and especially for me on the receiving end. I got just as sick and tired of explaining myself in the quest for understanding, as I did hearing my daughter explain herself.
I think it's 'outtolunch' who said explaining opens the door to negotiation. I got tired of negotiating personal power.