The General Lambert referred to in quot. 1680 was the Parliamentarian commander John Lambert (1619-83), who played an important role in Cromwell's military victories over the Royalists in the English Civil War.
I remember one sayeing of generall Lambert's, that ‘the best of men are but men at best’.
[1680 J. Aubrey Letter 15 June in Brief Lives (1898) I. 12]
We can but repeat to ourselves the saying, ‘The best of men are but men at best’.
[1885 T. Harley Moon Lore 191]
Related to: human nature; virtue
Bibliography of major proverb collections and works cited from modern editions is available here.
