Whenever you read about stories like this- (if you don't want to click the DM link, the URL is pretty much ronseal):

http://www.dailymail.co.uk/news/article-3302972/Fantasist-lorry-driver-lied-family-15-YEARS-SAS-hero-wife-died-cancer-believing-him.html

Also this muppet- http://www.dailymail.co.uk/news/article-3041696/Wife-discovered-cheating-husband-s-secret-second-family-tagged-Facebook-doing-Ice-Bucket-Challenge.html

What on earth makes people get into this level of lying to their families? And how good a liar would you have to be to get away with it? Got sny good examples? Really small town/local/seedy ones would be appreciated, thanks.