“We always know or it wouldn’t be penance.”

Dr. Joan Watson : Do you close yourself off to people and deny yourself things that might bring you pleasure not because it makes you a better investigator, but because it’s some sort of penance?
Sherlock Holmes : Penance?
Dr. Joan Watson : For what happened in London, being addicted. I don’t know, I guess it just occurred to me that it might be something that someone might do and not even know it.
Sherlock Holmes : You always know it, Watson. If you didn’t, it wouldn’t be penance.

— “While You Were Sleeping”, Elementary (01×02)