It's always a mistake for writers to bend the truth; readers will instantly notice. It's also obvious when they
let their views interfere when depicting character. A writer may disapprove of swearing, smoking, and certain political views, but if all the 'good' characters behave in ways he approves of he'll find it terribly limiting.Having a character do something nobody ever would in order to advance the plot is a seriously bad idea.
Follow the character, change the plot. Unless one's name is Agatha Christie, that is. It worked for her. Last week I listened to Murder in Mesopotamia, and the plot had me yelling at the radio, "What? What? WHAT?" It hinges on a woman who has been married to her husband for two years not realizing he is the same man she was married to fifteen years before. Now I'm not good at remembering faces myself, but even I might be relied upon to spot that husband #2 was husband #1, lightly disguised by a change of name and a Swedish accent.Though truth is good, writers need to be careful when adding undigested chunks of their lives to a novel. For some curious reason, that's always the bit readers pick on as being implausible, and it's no good protesting that it really happened to you. I remember on YouWriteOn criticizing a thriller because of the gorgeous personality-free female who seemed like just another bit of the hero's kit. The writer emailed me to say she was based on a real person he'd known. Problem is, even if he put a footnote in the finished book to that effect, it still wouldn't make the character believable.
So to sum up: we must tell the truth, but transform it into fiction first; never foist our prejudices on our characters; show life as we see it. No cheating.