18When the 1 is the parent
As a parent, a 1 sets the standard and expects it met: encouraging when you try, impatient when you do not. Children of a 1 learn independence early and need to hear that they are loved for who they are, not what they achieve.
As a child, an 8 wants to be in charge of something, and will negotiate. Give them real responsibility and real consequences, and they flourish.