Here’s Dr. Johnson on the dangers of quoting others in a commonplace book:
“the pleasure of wantoning in common topicks is so tempting to a writer, that he cannot easily resign it; a train of sentiments generally received enables him to shine without labour, and to conquer without a contest.” – Samuel Johnson, The Rambler, No. 2, ‘The necessity and danger of looking into futurity’. 24 March, 1750. Link
There’s some irony in quoting him, but it’s in the service of pointing out that Johnson’s essays in The Rambler are well worth a read.