Not see the wood for the trees
Definition 1 of 1
Pro Tip 1/3Detail Obsession
Emphasizes missing a broader issue due to focus on smaller, often less important details. 
When editing your essay, don't just focus on punctuation and miss grammatical errors; don't see the wood for the trees.
Pro Tip 2/3Analytical Thinking
Implies a need for a more analytical approach to see the whole situation clearly. 
As a project manager, make sure you're not seeing the wood for the trees by only concentrating on minor issues.
Pro Tip 3/3Warning Sign
Often used as a caution to suggest that someone may be missing an important aspect. 
You're adding features to the app, but not seeing the wood for the trees regarding user experience.