Wrong end of the stick 

An English idiom meaning to get something wrong by one's approach by making stupid assumptions. To think that something you've been offered is the opposite of what it is. To confuse left and right. To turn an ability into a disability, a solution into a problem.

The wrong end, as opposed to the right end of the stick.

It goes back to the medieval, when people use staffs, or a general purpose stick. One end would be held by its owner.

The right end of the stick is the driving seat, the nice, clean, comfy end.

The wrong end is the dirty, ugly pig-swill stirring, beating-dealing, non-walking-enhancing end.

Picking up another's stick by the wrong end is the sign of an idiot, it often signifies a favour turned into a curse by the recipient by of their foolish eagerness to play the game.

"Nice Rottweiler" said Rufus. I told Rufus the guard dog was having a bad day today, had been growling a lot. What did he do? He went skipping right up to it, tried to cheer it up "oooh poor doggie" and it bit him in the face. Totally got the wrong end of the stick.

Wrong end of the stick by Horton Cum-Studley February 6, 2012