Nietzsche is saying that for each human, there exists at least one thing that he or she cannot resist. And it’s inevitable.

There are no doubt a number of irresistible items, people, artwork, etc that can be resisted. Maybe it takes a lot of character or will power. However, that is saying something a little different.

However, I think that doesn't go far enough. As we dig deeper into the ramifications of the metaphysics behind this quote, we'll discover that that it is not limited to just humankind. All animals, plants, all living entities and perhaps even more should be covered. But more on that later.