Since my childhood, I’ve had a taste and a need for writing in code (so I could vent about my crushes without the risk of getting caught).
Since I didn't know another language yet—and even if I did, it wouldn't have served my purpose, as anyone who spoke it could still access my secrets—I quickly turned to something I didn't even have a name for at the time: a Monoalphabetic Substitution Cipher1.
'A' was a star, 'B' was a rune, the letter 'C' was a waxing moon, and so on.
And just like that, it was done. Now, all I had to do was copy the substitution table and give it to anyone I wanted to share my secrets with.