the tail wagging the dog
The smallest or least important part of something in control of the larger or more important elements; a reversal of typical roles or dynamics of power. They reorganized their entire weekly schedule just because their son likes to sleep in late. Talk about the tail wagging the dog. Their group is small but very vocal, so be sure that management doesn't give in to their demands. We don't want the tail wagging the dog, after all.
the tail wags the dog
the less important or subsidiary factor or thing dominates a situation; the usual roles are reversed. 1997 Spectator What is wrong is the almost total lack of artistic leadership, the administrative tail wagging the dog.