Not all intellectuals are introverts, but I would wager that all introverts are in fact intellectuals.
I'll use myself as an example.
If I'm not learning something new, I'm probably bored out of my mind.
And if a book, TV, or my phone aren't readily accessible -- to consume documentaries and other educational content, of course -- then I have no choice but to depend on my thoughts to pass the time.
Such thoughts might encompass:
- How the history or psychology book I'm currently reading might end, or what tome from my bookshelf I'll grab next
- How the pandemic might factor into consumer spending patterns going forward
- How many/which people have lived in my condo since the property was built
- Why certain people in my orbit behave the way they do