It is obvious when an actor has put work into prep and...

It is obvious when an actor has put work into prep and research and understanding their character, and they're making choices, because that's what happens when you take the time - or have the time - to really think about the material, but that only accounts for about 60% of what happens on the day. When you're in the moment, you throw it all away. Well, you don't throw it all away, but it's in you now, and everything is reactionary in that moment and you have to be honest and present and listening.