I say "know nothing" quite deliberately, because anyone who has any knowledge of sociology would know about Erving Goffman's Presentation of the Self in Everyday Life, published way back in 1959, and its revelation that all human beings have public and private personas, which often are in disagreement with one another. A waiter smiles at a difficult diner, takes the order, then curses him out when he places the order with the cook behind the counter. This is human nature - and, in the case of the waiter and everyone else, it doesn't prevent the waiter from doing his job, or even get in the way of that. To the contrary, it enables the waiter to be professional in his public sphere and do a better job.
In 1985, my friend and fellow Media Ecology New York University PhD graduate Josh Meyrowitz applied Goffman's analysis to politics in No Sense of Place, and demonstrated how front and back regions are the lifeblood of all successful politicians and leaders. Again, human beings require the private space to think out and explicate their positions to themselves and their families and closest advisors, before bringing them out to the public.
This is what Hillary was referring to when she cited Lincoln's differing public and private positions when he was working to get the 13th Amendment and its abolition of slavery through Congress. We already know that Hillary was familiar with media theorist Marshall McLuhan - see Gail Sheehy's 1999 Hillary's Choice and my own McLuhan in an Age of Social Media - and the timing would certainly have been right for her to have encountered Goffman's book in her Wellesley classes.
As in every other issue in this campaign, we have a choice between a knowledgable, serious thinker in Hillary Clinton verses an ignorant, lying bully in Donald Trump.