IN his Pentagon office, Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, has a picture of a war memorial in a working-class neighborhood of South Boston, his hometown. Dedicated in 1981, it commemorates local troops killed in Vietnam: 25 young men, several of them friends since childhood, died in combat there. Inscribed at the bottom of the polished black granite surface are the words “If you forget my death, then I died in vain.”

Few sentences better distill the spirit of Memorial Day. On Monday, President Obama is expected to place a wreath at the Tomb of the Unknown Soldier in Arlington National Cemetery, where, since 1864, more than 400,000 fallen troops have been interred. He may also pay homage to the troops still fighting in the nation’s two longest wars, in Iraq and Afghanistan — neither officially declared, neither actually over.

For those who have lost loved ones in battle, a different and quieter sort of memorializing is likely to take place in homes, churches and neighborhood cemeteries. “I miss you” posts will be left on Facebook pages remembering lost sons and daughters. Veterans will gather with their former units, recalling buddies over beer and burgers. Parents, children and spouses will lay wildflowers, notes and bottles of liquor near simple grave sites in remote towns. These are the places where so many service members come from and where so many return to in death.

Created after the Civil War, Memorial Day is an odd holiday, at once a solemn commemoration of those killed in war and a day of beach outings and backyard barbecues celebrating the start of summer. Rarely does it serve as a time to reflect on the policies that led to all those deaths.