As I start writing this it is 11:11 on Remembrance Day, the moment of silence on the anniversary of the end of the Great War in 1918, the "War to End All Wars", the war too horrible to repeat, the day to remember that. The day to remember the sacrifices and the horror and to not do it again.
"Lest we forget" is from Rudyard Kipling's poem Recessional. Written for Queen Victoria's Diamond Jubilee as a reminder of the impermanence of empires in the grand scheme of things. It's the same sentiment as Carl Sagan's "Pale blue dot" quotation: