Do the terms "preposition," "verb," "article," and "modal verb" sometimes stump you? Typically, students are taught the word "preposition" in 1st grade. I don't know about you, but I'm pretty sure that if I had seen that long word at the top of a worksheet in 1st grade, I would have skipped right over it, coding "preposition" as a long word that simply did not fit in my schema of the world.
Fast forward to middle, high school, and college, and I see that many native speakers often find one or more grammatical device or structure challenging. Grammar lessons learned in elementary school...