On truth in fiction

In a lecture at Emory,  Umberto Eco  said (roughly) on truth in fiction:

the statement “‘Superman is Clark Kent’ can never be challenged” whether the statement “‘Hitler died at a Berlin bunker’” is only (very) highly probable.

some thought on this seemingly semantic game leads to a number of important services of fiction to our life. One of them is, one can argue, the definition and expression of human qualities. I doubt non-fiction, often no more than an enumeration of ‘(very) highly probable’ facts along with inaccuracies introduced by the choice of words, is as appropriate.

How can one learn about qualities like introversion, compassion, loneliness, irrationality from non-fiction?