They say the camera never lies, but it never tells the whole truth either. You think you can see what’s real but there are all sorts of things you can’t see just beyond the frame of the photograph and beyond the moment when the photograph is taken. That happy smiling person you can see may have troubles in their life that you know nothing about, that idyllic scene may have mountains of rubbish and a power plant just out of shot making it a nightmare wasteland instead of a beautiful landscape.
There is always something missing even in the fragments of our own lives – we can never know the whole story that makes up any truth. It is only as we perceive things at the time that we make our own truths.
Truth is made up of many fragments and they are all subjective. Your truth is not my truth. My perception of things is not your perception of the same things.
It will be the same for our story characters. What one character understands as the truth won’t be the same as another character’s understanding. This leads to conflict and misunderstanding.
If everyone presumes that another person knows something that is known to all the others no one thinks of telling that other person. Consequently when that other person finds out what everyone else knows it can come as a shock to them and alter the way they see things and what their subsequent actions and reactions will be.
You need to ask yourself ‘what does one person know that another doesn’t’, ‘how does that character find out what the other person/people know’, and ‘what happens when they find out’?
This might be a bit of a philosophical discussion but you need to have it when writing your characters to make them seem real.