A lot of people quote Jean-Jacques Rousseau as saying, "There is nothing better than the encouragement of a good friend". However, I have been unable to find where this comes from.
This is from a letter by Katharine Butler Hathaway:
I thank you for your letter. It was generously written and beautiful, better than Thomas à Kempis because it is not too insistent upon things which are impossible to us. I cannot draw myself away to the realms of joyous angels. I am too much in love with the earth, even its woes and ugliness. I have always had a haunting distrust and fear of comfort and warmth because they seem to me a coating a crust which quickly makes one dull to the reality of real things—like death. It seems to me that the true proportion of realities is that which one must see in the hour of death. If I could only constantly keep that proportion in my mind, I think life would be much greater. But this is hardly better than the sentimental, religious babblings of some old ladies I know. This year I think I will study some philosophy—history of ancient philosophy—and really know a little about it.
It was good of you to remind me of my youth. I have felt as if I’d lived forever. There is nothing better than the encouragement of a good friend.
Katharine Butler Hathaway (21 September 1912). Letter to Catharine Huntingdon. In The Journals and Letters of the Little Locksmith (1946), pp. 61–62. New York: Coward-McCann.
Hathaway is best known as the author of the memoir The Little Locksmith (1942).
The quotation was correctly attributed to Hathaway in Edward Murphy (1981), 2,715 One-line Quotations for Speakers, Writers, & Raconteurs, p. 69, but the stripping of the attribution to a less famous writer (Hathaway) and its replacement with an attribution to a more famous writer (Rousseau) is typical of the way quotations are treated. Elsewhere on Literature Stack Exchange you will find spurious attributions to Mark Twain, Franz Kafka, Charles Darwin and many others.
The earliest attribution to Rousseau that I was able to find is in Martin van der Mandele (2009), Changing the Leopard’s Spots: Renewal of the Professional Firm, p.255. This book also has a quotation wrongly attributed to Darwin on page 17.