Reading Fiction vs. Non-Fiction as Literature

As Dr. Williams points out in his comment on my blog (see An Independent Woman Desiring Liberty), we cannot assume Ann's narrative as absolute truth.  It occurs to me that reading non-fiction is remarkedly different from reading fiction in that we must ALWAYS assume an unreliable narrator.  In literature, unless we are given a reason to assume unreliable narration (i.e., Jekyl and Hyde), we usually analyze narration as face value.  If a heroine says she was coerced into marriage, then we look at the coersion--but in non-fiction, we question whether she was coerced at all.  I realize this is not absolute, so please take my comments as general.

Another thought: It is ironic that literature, in which we sometimes we assume a reliable narrator, is fiction, whereas criminal narratives, if fiction, is based on some truth and we assume an unreliable narrator.