Suppose a person from our time is somehow (unintentionally) transferred to Western Europe during the late Middle Ages (circa 1300-1400). In a universe that allows multiple timelines, natural or physical reasons do not prevent him from making any actions.
He doesn't know how he got there (or when/where is he, at least in the beginning), nor does he have anything from the future with him (wakes up in local clothes).
For the sake of story, let's assume this man is educated, talented and relatively young & healthy (i.e. has time to do things). Moreover, suppose that he is ambitious and really wants to change the world, yet accepts his fate and does not search for a way to go back.
Finally, this person is lucky, so he won't be killed/enslaved/whatever immediately, but rather get the chance to learn the local customs and rise to a position of (relative) power quickly.
Now, the question is - can this person significantly impact the technological progress of the civilization (and with it the history, of course)? Or would his knowledge largely die with him?
After all, late Middle Ages Western Europe has, in theory, the resources and tools to create quite a few technical innovations (a steam engine comes to mind). But, on the other hand, he would probably find very few people who understand his line of thought.
Again, let's assume that he has a great starting position and that most things go in his favor (within realistic boundaries).