My purse doesn't listen

Why is it that when I sling my purse over my arm while getting out of the car it doesn't stay? Why must it always slide down my arm almost causing me to drop whatever is in my hand (usually a drink of some variety - Coke, Iced Tea, etc.)? And why, oh why, doesn't it listen when I tell it to stay? Seriously. This happens almost every day. And no matter how much discussion I have with my purse before getting out of the car, it fails me.

Obstinate purse. You do not please me.