Fall between two stools
Definition 1 of 1
Pro Tip 1/3Choosing Sides
If you try to please everyone in two opposing groups, you might end up pleasing no one. 
He tried to support both teams, but fell between two stools.
Pro Tip 2/3Indecision Risk
Being unable to decide between two options can lead to failure in achieving either goal. 
By not choosing a clear career path, she fell between two stools.
Pro Tip 3/3Moderation Caution
Sometimes, trying to find a middle ground or compromise can result in an outcome that is unsatisfactory for all. 
In trying to mediate the argument, he fell between two stools.