I understood the concept of "ex" as in ex-girlfriend, but not as in ex-con (convict). I did know what a "con artist" was so when I combined my limited knowledge of the two, I thought an ex-con was not someone who was recently paroled from prison, but someone who used to lie an awful lot.
A childhood belief about criminals

others believed things like this
- I used to think a con artist was someone who painted pictures in prison.— Brandon Campbell
- I used to believe when a person was convicted of a crime and sent to prison, his lawyer went to prison, too.— Tara
- I thought "prison" and "prism" are the same words as each other.Anon
- my uncle got sent to prison on the Isle of Wight. I thought that he had been sent into exile.— nns
- when i was little, i thought that a con artist was a person that painted pictures of people commiting crimes— kimkim
- I thought the women in Prisoner Cell Block H were actresses banged up in prison themselves.— Reb Kean