Properly read, Plato's allegory of the cave in the Republic is a response to the question you've articulated. Kant noted as much, and when not resolved with dualism (which flowed from Plato through Descartes to the modern day), this allegory offers powerful insights. I love these topics, have been swimming in them recently, so happy to talk more, just email me (info in profile).
"I thought I was the originator of many my out-of-the-blue thoughts, and I found out that's not true. Am I actually the originator of the thoughts at the next level up?".
I think some people who have never meditated, while they admit to having thoughts just hit them randomly sometimes, they'll nonetheless feel that many of their truly out-of-the-blue thoughts were conscious choices to switch gears or pull on an interesting thread. A meditator might label the same low-level thought as "random", but a non-meditator would say "I did that". Can a meditator similarly be fooled, on a different level?