Unlike Phil Michelson, I have no childhood experience teaching me to golf left-handed by standing opposite a right hander to learn the swing techniques.  Certainly so with golf, since I didn't pick up the game until I was in my 30's.  I cannot remember any childhood experience, favorite player or whatever that guided me towards swinging a baseball bat left handed.  I guess this isn't a bad thing now since so many golfing products are available for lefties compared to days past. 
Pretty much everything else I do right handed. Write, throw a ball, swing a tennis racket, use my computer mouse, etc.  Although I can do some of those things left handed, they are not as good, strong or reliable.  The golf swing (and baseball bat) just feels weak and terribly clumsy if I try to do them right handed.   If it requires strength, dexterity, stability, or coordination, I always favor my right hand/arm. 
My wife, a lefty through and through, swings her golf club right handed.  But our son, a really good golfer, is right handed at everything.
So what gives here?  Is it a learned and practiced movement which forces/favors left over right?  Is it a left brain versus right brain thinker thing going on?   I'd be curious to hear what other golfers experience/teaching/example has led them to being a  lefty/righty.