Because dude, you know what? Every story ever written is broken. All of them. People don’t like stories because of what they don’t do wrong.
They like them because of what they do right.
Adams is not only speaking to Trumbull in that scene. He is speaking to us, the creators of the series, and to our audience, warning us that history ceases to be real after the last man who remembers it has passed–and very possibly even a good while before that. “Truth, nature, and fact” should indeed be our guides at all times. But who defines truth? (Even Pontius Pilate failed to obtain an answer for that question from the one man who might know.) And while facts are stubborn things, they can also be rather slippery as well, serving a variety of purposes and dependent on the person wielding them. Adams and Jefferson both lived long enough to see the revolution recounted, analyzed, and reinterpreted by countless commentators. If our miniseries sends people back to the first-hand accounts, then we have achieved our purpose.