Gen Milley's background:
Milley earned his commission as an Armor officer through Princeton's Army Reserve Officers' Training Corps program in 1980 and spent most of his career in Infantry assignments. He has served in the 82nd Airborne Division, the 5th Special Forces Group, the 7th Infantry Division, the 2nd Infantry Division, the Joint Readiness Training Center, the 25th Infantry Division, Operations Staff of the Joint Staff, and as a Military Assistant to the Secretary of Defense in the Pentagon.
General Milley has had multiple command and staff positions in eight divisions and special forces throughout the last 39 years to include command of the 1st Battalion, 506th Infantry, 2nd Infantry Division; Milley commanded the 2nd Brigade Combat Team, 10th Mountain Division (Light) from December 2003 to July 2005, served as deputy commanding general for operations of the 101st Airborne Division from July 2007 to April 2008, and was commanding general of the 10th Mountain Division from November 2011 to December 2012. He then served as the Commanding General of III Corps, based at Fort Hood, Texas, from 2012 to 2014, and as the commanding general of the United States Army Forces Command, based at Fort Bragg, North Carolina, from 2014 to 2015. He was appointed chief of staff of the Army on August 14, 2015.
This sounds to me like a bio of someone that is pretty smart and brave but not enough for tough-guy Carlson.
Apparently he doesn't seem to have a whole lot of respect for the US Army if he thinks that they'll have stupid cowards hold all of these positions and appoint them as Chief of staff.