“I did not enjoy being secretary of defense,” Mr. Gates writes at one point in the book. Fair enough; he could have retired after serving out the remainder of President Bush’s term. He didn’t. “People have no idea how much I detest this job,” he quotes from an email he wrote in mid-2008, trying to scotch rumors that he would serve under the next administration. Fair enough; he could have turned down Mr. Obama’s offer when it was made. He didn’t. “If you want me to stay for about a year, I will do so,” he told Mr. Obama after the 2008 election. Fair enough; he could have kept the promise to the letter. He didn’t; he stayed on for another 29 months.

Those are choices Mr. Gates made for his own reasons. Serving as secretary of defense, after all, isn’t really a duty; it’s an honor and a privilege.

Honors and privileges, however, do have duties. One is: Don’t treat them as a burden. Another is: Don’t betray the confidence of those who bestow them on you. A third is: Resignation is honorable, but the tell-all memoir against a president still in office is not. When people wonder why Mr. Obama only seems to listen to Valerie Jarrett and other hacks, maybe it’s because at least he can count on their loyalty.

Deep in the book Mr. Gates writes that “A favorite saying of mine is ‘Never miss a good chance to shut up.'” His memoir is one big missed chance.