You don't appreciate a faithful husband when you've got one,' said Tommy. 'All my friends tell me you never know with husbands,' said Tuppance. 'You … - Agatha Christie

For in the long run, either through a lie, or through truth, people were bound to give themselves away …

Lie is more worth living, more full of interest when you are likely to lose it. It shouldn't be, perhaps, but it is. When you're young and strong and healthy, and life stretches ahead of you, living isn't really important at all. It's young people who commit suicide easily, out of despair from love, sometimes from sheer anxiety and worry. But old people know how valuable life is and how interesting. - Jane Marple

Who are you? You don't belong to the police?'
'I am better than the police,' said Poirot. He said it without conscious arrogance. It was, to him, a simple statement of fact.