the tail wagging the dog
US /ðə teɪl ˈwæɡɪŋ ðə dɔɡ/
UK /ðə teɪl ˈwæɡɪŋ ðə dɔɡ/
1.
a situation in which a small or less important part of something controls or dominates the whole thing
:
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Allowing a minor issue to dictate the entire project budget is a classic case of the tail wagging the dog.
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In this company, it often feels like the tail is wagging the dog, with junior staff making decisions for senior management.