Those of us who have commanded combat outfits in coin understand Wilf's statement that soldiers are not diplomats. Coin experts may retch when this is said but basically, fundamentally it is a statement of fact. Combat soldiers stand posts, they shoot, they pull security, they do raids, they patrol, they secure infrastructure projects, etc. The notion that they are diplomats is self-serving fiction. It briefs well but beyond that it is pure nonsense.
This attitude contributed greatly to our downward trend in OIF. Fortunately for our nation it was reversed by an officer who understood that engaging in diplomacy with the locals is not a self serving fantasy, it is absolutely essential. Soldiers are more than capable of engaging with the local populace to identify and help resolve their problems, thus helping develop trusting relationships with the locals that also enable Soldiers to garner intelligence based on that relationship.

If Soldiers are only capable of guarding infrastructure and saluting their red coat officers who have no faith in them (I realize this only applies to a small percentage of our officers, but unfortunately a damaging percentage), then we might as well empty our prisons and fill our ranks with category four soldiers, because we don't need well behaved smart kids capable of solving complex problems like we have now, we just need grunts who do not interact with their environment, but can shoot when so ordered.

Shifting from combat to COIN is not that difficult, if it seems too hard, then the training is inadequate because numerous Armies do it, have done it, we have done it -- it just isn't that difficult.
Words of wisdom, as are,

Be careful how we train -- too much training time spent on building other peoples Armies or nations will lead to a US Army that is not competent at its own primary mission.

We need to be able to do COIN adequately (as opposed to superbly); we do not need to let it drive the train...
It isn't that hard, even an officer can figure it out if he has a patient NCO that doesn't mind mentoring him. Nor do we have to be that good at it, but we sure as how have to understand the character of the fight we're in.