Well, from my personal experience, I know the curse does work and is not simply a mind thing because there was a time when I pirated their books (which is not okay and I don’t pirate anymore), and I found out about the curse one day through divination before I even knew that they curse pirated downloads. But I also found out through divination what @DarkestKnight said, it’s not a destructive curse. Which was confusing to me at the time and I could not tell the purpose of the curse from the reading. But like you, I still had success with the magick regardless, but now that I bought their books I can definitely tell an improvement in the effectiveness of the magick.