You were a non-reader, preferring to watch movies and series rather than touch a book.
But then, someone recommends a novel they think you’ll like, you flip through it and love it!
In case it’s the first part of a trilogy or series, and you decide to read the whole series (or at least read all the parts you get your hands on and, in case you can’t get your hands on the last ones, you decide to look for spoilers on the internet).
That was my experience with Warriors by Erin Hunter.
What’s yours?
Well, Harriet the Spy. But if you mean like “serious business” after elementary school lol LOTR was probably the first of those.