Rumsfeld acknowledges that he erred in a March 2003 interview with ABC's George Stephanopoulos, when he said that despite the failure to find weapons of mass destruction shortly after the invasion of Iraq, "we know where they are."
Rumsfeld writes that he meant to say that U.S. intelligence agencies knew where "suspect sites" were, not that anyone knew definitively where the actual weapons were. But it was a misstatement Rumsfeld's critics seized on, for the duration of his service in the Bush administration and beyond.
"My goodness, the intelligence was certainly wrong," he told Sawyer.
He wouldn't entertain questions about whether he would have acted differently had he known the truth about the lack of WMDs in Iraq.
"I have no idea. I have no idea," he said. "What you know today can help you on things you're thinking about tomorrow. It can't help you with things you were thinking about back then. Back then there was reasonable confidence that he had these weapons."
Rumsfeld dismissed the criticism he got from a collection of retired military leaders in 2006, as the war effort in Iraq was going poorly. The former officials took the extraordinary step of calling for Rumsfeld's resignation, citing what some viewed as an imperious leadership style as well as missteps in leading the Iraq war.
"It was a group of people who were disgruntled. And I've never worked with most of them. Fact, I'd not met some of them," Rumsfeld said.
Rumsfeld offered no apologies for his notoriously brusque management style, saying he would not accept criticism for asking "tough questions."
"Oh, the poor people, I terrified them. My goodness, come on," Rumsfeld said. "These are people with stars on their shoulders. They're people who are patriots. They're people who've fought battles. And they weren't terrified or intimidated."
He expressed disappointment that Bush also felt he was sometimes too abrupt with military leaders and members of his staff.
"You know, it's too bad," Rumsfeld said. "He believed -- apparently believed -- the mythology that was perpetrated in the press."
Rumsfeld's book also sheds light on personal struggles that sometimes came at moments of great professional challenges.
His son, Nick, was battling drug addiction around the time of 9/11 and had gone missing earlier that summer. Just two weeks after the terrorist attacks, Rumsfeld writes, Bush offered his defense secretary comfort on the subject of his son, during a private meeting in the Oval Office that brought Rumsfeld to tears.
"He reached out and said, you know, 'Tell me about it,' " he said. "And you start talking about it. And it's hard to talk about it, because it's -- a wonderful human being, that you love. And you want it to be better. And he is, God bless him."
The book takes its title from a famous news conference where Rumsfeld lectured the press about the limits of intelligence gathering, musing aloud about "known knowns," "known unknowns," and "unknown unknowns."
Though the locution has been used to mock him at times, Rumsfeld said the phrases are an apt summation of his career and experiences.
"It is a thread that runs through my public service," he said, "that there are things we don't know we don't know. And nobody knows them."
"Proceeds from the sales of Known and Unknown will go to the veterans charities supported by the Rumsfeld Foundation."
"World News with Diane Sawyer" will have more of Sawyer's exclusive interview with Rumsfeld tomorrow on "World News" and on ABCNews.com