This passage appears at the close of Housman's autobiography, The Unexpected Years. Housman created the decorated initial for his A Doorway in Fairland — George P. Landow.
f all the strange oppositions of life the two strangest are what we remember and what we forget. How many great and important things important in their influence upon one's after life has one not perhaps utterly forgotten. Strange that one should, if they made one what one has become to-day. And yet as one knows nothing of one's first begetting, out of which came life and breath, so of these sequent begettings there is no outward expression that one can take hold of and recognize and trace to its source in things said or things done.
And then, on the other side, the things that one remembers: the little things that come stepping into life so quietly, to remain so unexpectedly permanent not so unexpected in their happening as in their effect. Why does one remember certain intonations, gestures, actions one's own or other people's, so trivial in character, so empty of all practical result that one can see: they were of no importance at the time, or beauty or interest; but there, minute particles of a past life inseparable from memory, they stick beautiful in their mysterious tenacity though with no other beauty for which we could desire them; insignificant essentials in a life which we call our own but cannot control or isolate from that web of life into which everything goes spun nothing we can do will away with them. 
Housman, Laurence. The Unexpected Years. London: Jonathan Cape, 1936.
Last modified 19 November 2012