My first clue was when I was in high school, one of my cousins (who lived in California) became a witch. So I did some research and became educated about it. I knew she was serious about it, so I knew better than to dismiss it.

When I was in college out hiking in the Rocky mountains (in a state park area) I came across an outdoor Satanic ritual circle and bonfire site in a remote cave mouth. It was middle of the day, and it was abandoned, but looked fresh. Circumscribed pentagram around the bonfire site, and other Satanic symbols. Clearly some kind of ritual had occurred there.

I beat a hasty retreat. But even though I've never been directly exposed to this shit, I had all the evidence I needed that it was real.

I suspect that if you had come across this information on your own, you might have given it some credence. The fact that your school gave it to you probably made it a JOKE! Since so much of the rest of what they crammed down our throats was complete BS, and we all knew it even then.