“I learned more in the six or seven hours of this experience than I had learned in all my years as a psychologist.”

Quoted in "THE CONGRESS: Education of a Senator," http://content.time.com/time/magazine/article/0,9171,780085,00.html Time magazine ( 17 January 1949 http://books.google.com/books?id=8-jVAAAAMAAJ&q=%22I+learned+more+about+economics+from+one+south+dakota+dust+storm+than+I+did+in+all+my+years+at+college%22&pg=PA14#v=onepage)

Attributed to Plato in Confidence : How to Succeed at Being Yourself (1987) by Alan Loy McGinnis, this is probably a paraphrase of a statement which occurs in Letter of Advice to a Young Gentleman Leaving the University Concerning His Behaviour and Conversation in the World (1907) by Richard Lindgard: "Take heed of playing often or deep at Dice and Games of Chance, for that is more chargeable than the seven deadly sins; yet you may allow yourself a certain easie Sum to spend at Play, to gratifie Friends, and pass over the Winter Nights, and that will make you indifferent for the Event. If you would read a man’s Disposition, see him Game; you will then learn more of him in one hour, than in seven Years Conversation, and little Wagers will try him as soon as great Stakes, for then he is off his Guard."
Variants:
You can learn more about a person in an hour of play than in a year of conversation.
Attributed to Plato in Food Is the Frosting-Company Is the Cake (2007) by Maggie Marshall
You learn more about a person in an hour of play than in a year of conversation.
Attributed to Plato by former Alaska Gov. Sarah Palin, as quoted in "Aspiring philosopher Palin quotes 'Plato'" (9 July 2009) http://thinkprogress.org/2009/07/09/palin-plato/
Misattributed

Not found in Twain's works, this was attributed to him in Reader's Digest (September 1939): no prior attribution known. Mark Twain’s father died when Twain was eleven years old.
Disputed
Variant: When I was a boy of fourteen, my father was so ignorant I could hardly stand to have the old man around. But when I got to be twenty-one, I was astonished at how much the old man had learned in seven years.

The Irish News, 22/01/2005
On Classical Music

Source: Lady Midnight

Straits Times, 01/11/1991
Musician's life

Source: The Amulet of Samarkand

Thank Goodness! (2006)
Context: Friends were anxious to learn if I had had a near-death experience, and if so, what effect it had had on my longstanding public atheism. Had I had an epiphany? Was I going to follow in the footsteps of Ayer (who recovered his aplomb and insisted a few days later "what I should have said is that my experiences have weakened, not my belief that there is no life after death, but my inflexible attitude towards that belief"), or was my atheism still intact and unchanged?
Yes, I did have an epiphany. I saw with greater clarity than ever before in my life that when I say "Thank goodness!" this is not merely a euphemism for "Thank God!" (We atheists don't believe that there is any God to thank.) I really do mean thank goodness! There is a lot of goodness in this world, and more goodness every day, and this fantastic human-made fabric of excellence  is genuinely responsible for the fact that I am alive today. It is a worthy recipient of the gratitude I feel today, and I want to celebrate that fact here and now.