Claire tells Jamie that "history dictates" that the Scots will fail in their battle against the English. She of course knows this from her vantage point from the future - which says all of their work to break free of the English will be in vain. But Jamie counters that Claire has already changed history - as when, for example, she stopped an outbreak of smallpox in Paris with her knowledge of the illness garnered in the future 20th century.
But the problem with such examples is that they are unknown to us - that is, the viewers. We have no record of a smallpox outbreak in mid-18th-century Paris stopped by a woman wielding white magic or some kind of 20th-century knowledge of epidemics. Thus, while Jamie's examples may be impressive - at least, somewhat - to Claire, they aren't to us, upon any kind of more careful consideration.
In order for a time-travel story to be truly impressive about changing the past to change the future, it has to show us a future different from what we know. Otherwise, it can still be impressive, but it must do that in other ways.
As the conversation between Claire and Jamie continues, she says that their failures to change history and stop the English thus far, and their continuing to try, over and over again, is a sign of "insanity" - more precisely, Claire says "they say" it's a sign of insanity. Jamie's clever retort is "they" likely never heard of time travel.
Now, in our reality, the definition of insanity as "doing the same thing over and over again and expecting different results" is most often attributed to Einstein. Which is interesting, since Einstein certainly knew about time travel - at the very least, of its appearance in H. G. Wells' The Time Machine, which is the effective grandsire of all 20th- and 21st-century time-travel stories, including Outlander - which deserves credit for at least delving into these fascinating metaphysical labyrinths, if not (yet) coming even remotely close to resolving them. But that's ok - there's still time (travel).
See also Outlander 2.1: Split Hour ... Outlander 2.2: The King and the Forest ... Outlander 2.3: Mother and Dr. Dog ... Outlander 2.5: The Unappreciated Paradox ... Outlander 2.6: The Duel and the Offspring ... Outlander 2.7: Further into the Future
And see also Outlander 1.1-3: The Hope of Time Travel ... Outlander 1.6: Outstanding ... Outlander 1.7: Tender Intertemporal Polygamy ...Outlander 1.8: The Other Side ... Outlander 1.9: Spanking Good ... Outlander 1.10: A Glimmer of Paradox ... Outlander 1.11: Vaccination and Time Travel ... Outlander 1.12: Black Jack's Progeny ...Outlander 1.13: Mother's Day ... Outlander 1.14: All That Jazz ... Outlander Season 1 Finale: Let's Change History
Sierra Waters series, #1, time travel