I never have trouble keeping fact and invention straight.

Not to give too big of a spoiler, but I never find myself thinking, for example, Oh, remember that crazy time I stumbled on that closeted Republican candidate's sex tape?

In early drafts, one of the trickiest things for me to do was to realize that the techniques and devices that make readable and compelling nonfiction are not always identical to the ones that make good fiction.

If a reader believes that everything in nonfiction or history is just objectively true, I don't really know what to tell them, except that at least in fiction, the choice of what perspective and bias to tell a given story from - which is always a deliberate choice - is foregrounded and clear.