tail wagging the dog, the
A small or unimportant factor or element governing an important one; a reversal of the proper roles. For example, She found herself explaining the new therapy to her doctor—a real case of the tail wagging the dog. [c. 1900]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.