Missing part of an idiom or expression I heard "Have you lost the [something] you were born with"

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?

Solution 1:

One possibility is

Have you lost the little sense you were born with?

Sometimes little is omitted.

For examples of usage in published literature, see here and here.

Solution 2:

To paraphrase the 1907 American folk story Epaminondas and His Auntie, the saying is, "You don't have the sense you were born with."