Directionally Challenged » Head

Excessive head movement 
translates to excessive offline shots.

If your head moves to sneak a peek or whatever-is-happening-in-your-head to make it move, then your shots will go wayward.

Believe it or not, as soon as your head begins its excessive movement, your swing plane is affected. The clubface at impact will no longer be square and in the correct position for a crisp strike.

A quiet head allows the club to do its job without you getting in the way.