What is the reason?

I understand that the way the body deals with various injuries or diseases happen for a reason. You cut your finger and blood rushes to the cut and special cells clot the hole and the white cells get to work. Or you bruise something and red blood cells come in and pack the area bringing nutrients and oxygen rich blood. You sneeze to get rid of "junk" in your system. And you shit to...um, shit. But why on earth do humans get stiff necks? What is the point of that. I recently ended a four day stint with a stiff neck. Why? I dunno. Stiff necks are as usefull as waterproof tea bags, and just as dumb.