[Johnson] recommended to me to keep a journal of my life, full and unreserved. He said it would be a very good exercise, and would yield me great satisfaction when the particulars were faded from my remembrance. … He counselled me to keep it private, and said I might surely have a friend who would burn it in case of my death. [14 July, 1763]
He told me, that he had twelve or fourteen times attempted to keep a journal of his life, but never could persevere. He advised me to do it. ‘The great thing to be recorded, (said he,) is the state of your own mind; and you should write down every thing that you remember, for you cannot judge at first what is good or bad; and write immediately while the impression is fresh, for it will not be the same a week afterwards.’ [11 April, 1773]
James Boswell, Life of Johnson, ed. R. W. Chapman, rev. ed., (Oxford: Oxford Univ. Press, 1970), pp. 307, 513.