But we also want to point to two passages in his conversation with Morning Edition host Steve Inskeep that particularly struck us.
Speaking about the condolence letters he would write each evening to the families of fallen troops, Gates said:
"I was determined that these young people would not just become statistics for me. And so I started out by handwriting parts of the — of the condolence letters.
"And then — and even then that wasn't enough, I felt. And I so then I started asking that every time one of these packets came to me, that it'd have a picture of the — of the soldier or sailor, airman or Marine who'd been killed, along with the hometown news so that I knew, you know, what their coaches and their parents and their brothers and sisters and teachers were saying about them, so I felt like I had some personal knowledge about each one of them.
"And I would write those condolence letters every evening."
Asked whether that became difficult, Gates shared this personal memory:
"It didn't take too long. I think that quite honestly, in the — in those evening sessions, writing the condolence letters, there probably wasn't a single evening in nearly 4 1/2 years when I didn't — when I didn't weep."
At another point in the conversation, Gates says he "came to realize in the early spring of 2011 that my preoccupation, my priority had become protecting [the troops] from further sacrifice, perhaps at the expense of hard-headed objectivity in terms of the use of our military. And I was becoming emotional when I was around the troops and thinking about the troops. And all of that contributed to my decision on the specific timing that it was time to go."
He left the Pentagon in June 2011.
Gates says one of the toughest decisions he made while leading the Pentagon, was to extend the typical combat tour from one year to 15 months.
"I have no statistics to prove it," he said, "but I believe that those 15-month tours had to have aggravated the post-traumatic stress problem and probably the suicide problem. ...
"As one of my junior military assistants put it, 15 months brought into play the 'law of twos.' You miss two Christmases, two birthdays, two anniversaries and so on, and I think that had a consequence."