"You have to set the example at the top," Carter said on CNN's "New Day." "And so I always did. And when people didn't meet that standard, they needed to be fired. And so the profession of arms especially is about honor and trust."
He continued, "A mom whose son is in harm's way looks up and says, 'That man is exhibiting the kind of behavior that I can have some confidence in because my son or my daughter's life is in the hands of the decisions he makes.'"
He was asked about leadership in the context of a White House aide joking that Sen. John McCain's "no" vote against the nominated CIA director, Gina Haspel, doesn't matter because he is "dying."
"It was important to me not only for myself and my own conduct but to set an example for the troops," Carter, who served at the Pentagon for two decades and was President Barack Obama's final defense secretary, told CNN.
Carter, who is now the Director of the Belfer Center for Science and International Affairs at Harvard Kennedy School, recalled the praise that foreign leaders would bestow on American service members, due to their professional conduct.
"I'm always proud of our people, but I would go and meet foreign leaders. They would always say, 'Our military likes working with yours.' It's not just because they're awesomely capable, which is true, but it is also the way they behave, the way they conduct themselves. That's very important."