That is why most great love stories are tragedies.
Assumptions are dangerous things.
There is no detective in England equal to a spinster lady of uncertain age with plenty of time on her hands.
Things go entirely differently from the way you planned them.
It is the quietest and meekest people who are often capable of the most sudden and unexpected violences for the reason that when their control does snap, it goes entirely. (Hercule Poirot)
In old days the public didn't really mind much about accuracy, but nowadays readers take it upon themselves to write to authors on every possible occasion, pointing out flaws.