Adversity is a great teacher, but this teacher makes us pay dearly for its instruction; and often the profit we derive, is not worth the price we paid.
It's kind of part of human nature to want to know the truth or want to be in on the secret. For stories that focus in on that - like whodunits - it's easy to get drawn into.
I never practice before, I never work hours on a script. I just choose my characters and trust them, and after that, it's about the director taking your hand.

