They call him "Lefty".  A surefire Hall of Famer in the waiting.  A four-time major champion which includes three green jackets at The Masters and a PGA Championship in 2005.  But Phil Mickelson is missing one major.

A United States Open.

Many golf people wonder why Phil Mickelson hasn't won a U.S. Open.  It actually isn't hard to figure out.  Mickelson, for the most part, has been a risk taker over the years.  The U.S. Open doesn't reward risk takers.  The toughest test in golf rewards smart, placed shots, grinders and great putting on Saturday and Sunday.  Mickelson found this out on 18 in 2006 at Winged Foot when he shanked a drive and lost any hope of winning America's major.

And so here we are in 2013, at Merion Golf Club, where placement shots are needed.  Grinding is needed.  Great putting on the weekend is a must.  Phil Mickelson must do these things to win the U.S. Open.  Phil Mickelson must do these things because "Lefty" needs a U.S. Open to complete his great career.  His golf resume would look remarkably different if the toughest test in golf were added.  Think an NFL quarterback or head coach with two Super Bowl rings, not one.

Mickelson must stay the course this week at Merion and leave the tricks in the bag for another tournament.  Then maybe, just maybe, the toughest test in golf will no longer be Mickelson's toughest test of his career.

By:  Mike Lindsley, "Mid-Day with Mike," 1-4, Yankees pre/post game host on 104.5 The Team ESPN Radio.  Follow him on Twitter @MikeLSports.