Human motivation cannot be documented, at least not with any kind of finality. After all, we rarely understand our own motivations, and so, even when we write down what we honestly believe to be our reasons for making the choices we make, our explanation is likely to be wrong or partly wrong or at least incomplete. So even when a historian or biographer has a wealth of information at hand, in the end he still has to make that uncomfortable leap into the abyss of ignorance before he can declare why a person did the things he did.
