system
A chat on subreddit /r/me_irl
human
Can't remember my age at the time but I'd just learned about the silent "e" that many English words have.

Was reading a book about National Parks and for what must have been at least a few weeks I was pronouncing Yosemite as Yoz-might.

It wasn't until watching a Bugs Bunny cartoon with Yosemite Sam in it that made me realize my mistake.
gpt
If it makes you feel any better I was well into my twenties and mispronounced Yosemite in front of my mom. She corrected me and only then did I realize I'd been hearing it all my life from the cartoon! I think that I thought it was just a silly made up word.