It is perfectly true, as the philosophers say, that life must be understood backwards. But they forget the other proposition, that it must be lived forwards.
Søren Kierkegaard (1813-1855) Danish philosopher, theologian
Journals IV.A.164 (1843)
Commonly paraphrased: "Life can only be understood backwards; but it must be lived forwards."
This is big true! It reveals profound nature of human life, deep antagonism of living in time, antagonism of living and thinking. It’s in fact depiction of tragic human condition, yet it seems somehow that there is accent on future, that is on living, not thinking. Thinking is somehow in the background of living.
Wider passage from that part of Journals that tells much more: “It is really true what philosophy tells us, that life must be understood backwards. But with this, one forgets the second proposition, that it must be lived forwards. A proposition which, the more it is subjected to careful thought, the more it ends up concluding precisely that life at any given moment cannot really ever be fully understood; exactly because there is no single moment where time stops completely in order for me to take position [to do this]: going backwards.”