“The first one has to do with whether a man knows what he is talking about, whether what he says has some basis or not. And my trick that I use is very easy. If you ask him intelligent questions — that is, penetrating, interested, honest, frank, direct questions on the subject, and no trick questions — then he quickly gets stuck. It is like a child asking naive questions. If you ask naive but relevant questions, then almost immediately the person doesn't know the answer, if he is an honest man.”

ibid, 114-5

Source: Empty Cages (2004), Ch. 4

Shades of Grey (2010), p206

Source: Daughter of the Blood

[John J. B. Morgan and T. Webb Ewing, Making the Most of Your Life, 2005, 75 http://books.google.fr/books?id=5i-JlfkMEUUC&pg=PA75]
Attributed
Variant: No man really becomes a fool until he stops asking questions.

Source: Why Men Love Bitches: From Doormat to Dreamgirl-A Woman's Guide to Holding Her Own in a Relationship

Then if you ask your grandmother whether she knew about Peter Pan when she was a girl, she also says, "Why, of course, I did, child," but if you ask her whether he rode on a goat in those days, she says she never heard of his having a goat. Perhaps she has forgotten, just as she sometimes forgets your name and calls you Mildred, which is your mother's name. Still, she could hardly forget such an important thing as the goat. Therefore there was no goat when your grandmother was a little girl. This shows that, in telling the story of Peter Pan, to begin with the goat (as most people do) is as silly as to put on your jacket before your vest.
Of course, it also shows that Peter is ever so old, but he is really always the same age, so that does not matter in the least.
Source: The Little White Bird (1902), Ch. 14

Source: Beyond This Horizon (1948; originally serialized in 1942), Chapter 2, “Rich Man, Poor Man, Beggar Man, Thief—”, p. 35; see also pages 31, 33