I am writing a story and my character is being scolded for doing something stupid. I have an expression on the tip of my tongue, but part of it keeps evading me! "Have you lost the [thing that keeps evading me] you were born with?" Is it the good senses you were born with? The brain you were born with? I can't remember and it is beginning to drive me crazy... Does anyone know the part I'm missing?
To paraphrase the 1907 American folk story Epaminondas and His Auntie, the saying is, "You don't have the sense you were born with."
I think it is 'the silver spoon in the mouth' that was lost. If they say so, it means you're not lucky.