We live, not as we wish to, but as we can.
ζῶμεν γὰρ οὐχ ὡς θέλομεν, ἀλλ᾿ ὡς δυνάμεθα.
Original text (Ancient Greek)
Notes from Wikiquote
Compare Terence, Andria, 805:
ut quimus' aiunt, quando 'ut volumus' non licet.
As the saying is, we do as we can since we can't as we would. (tr. J. Sargeaunt, 1918)