James Mattis, the retired four-star general who resigned as defense secretary on Thursday, has long been viewed as a legendary figure in the U.S. military. One particular story, told in 2003 at an ethics lecture organized by the Center for the Study of Professional Military Ethics, perfectly explains why former staffers saw Mattis as a "cult figure."
In 1998, a now retired General Charles C. Krulak had been preparing for an annual tradition where he delivered hundreds of Christmas cookies to post guards. On Christmas day at around 4 a.m., Krulak headed to Virginia, to the command center at Quantico. Once there, he asked the lance corporal who the officer on duty was.
"Sir, it's Brigadier General Mattis," the lance corporal answered, as Albert C. Pierce, a director at the ethics center, explained at the lecture.
"No, no, no. I know who General Mattis is. I mean, who's the officer of the day today, Christmas day?" Krulak asked with persistence.
General Mattis, the soldier repeated.
A short time later, Mattis appeared, fully dressed in his uniform complete with his sword. Krulak then asked the seasoned military leader why he chose to be on duty.
As Pierce explained: "General Mattis told him that the young officer who was scheduled to have duty on Christmas day had a family, and General Mattis decided it was better for the young officer to spend Christmas Day with his family, and so he chose to have duty on Christmas Day."
"That's the kind of officer that Jim Mattis is," Krulak later said.
Those who worked for Mattis recount many similar examples where Mattis put his team's needs ahead of his own. In his book, "One Bullet Away," former Marine captain Nate Fick describes his experiences with Mattis while in combat in Afghanistan and Iraq.
"No one would have questioned Mattis if he'd slept eight hours each night in a private room, to be woken each morning by an aide who ironed his uniforms and heated his MREs," he writes in the book. "But there he was, in the middle of the freezing night, out on the lines with his Marines."
Mattis' actions are a timeless reminder that even the toughest leader can embrace compassion. In fact, "Mad Dog" Mattis was known to caution leaders not to allow their passion for excellence to destroy their compassion for their subordinates.
After all, as Mattis once explained, our ability "to build trust and harmony" is as critical as our ability execute any task.
Like this story? Subscribe to CNBC Make It on YouTube!