before one knows it

before one knows it

1. rapidly (and sometimes unexpectedly)

   before you know it

• before you can say knife

• “before you know it” in Longman Dictionary of Contemporary English, Longman.
• “before you know it”, in Cambridge English Dictionary, Cambridge, Cambridgeshire: Cambridge University Press, 1999–present.
• “before one knows it”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.