I thought Jack was a nickname for Jackery ( like Zack and Zachary).
A childhood belief about names

others believed things like this
- I thought "Virgin Mary" was actually "Verge 'n Mary" and that Verge was a nickname for Joseph. — Rachel
- "She's got the Jack" by ACDC was "She's got the Clap".— Cybela
- Since the girls name Jackie is short for Jacqueline, I thought the boys name Jack was short for JackalAnon
- I used to believe that tornadoes were spinning jack-o-lanterns in the air bent on destroying my house.Anon
- I used to belive that Jack Frost was a real man! and that he came and painted frost on the windows at night.— Tom
- We had an antique lamp that I thought was hideous and for years I thought "Art Deco" was a synonym for ugly.Anon