Free Will in Slaughterhouse Five
The epitaph on page 156 states that free will was the deciding factor between Billy Pilgrim wanting to tell his wife about the war. Free will allow us to make the choice whether or not to tell people others about certain events that have taken place in our lives. We only know the reason behind our words and actions; free will allows us to put these thoughts out there in a coherent way. Trust involves another person, regardless if we trust him/her enough to share our experience with, it is our free will entitles us to keep quiet or not.