Not see the forest for the trees
Definition 1 of 1
Pro Tip 1/3Metaphorical Meaning
The phrase is a metaphor comparing the inability to see a situation's main point to overlooking a whole forest by focusing on single trees. 
When editing her novel, she couldn't see the forest for the trees, obsessing over commas and missing the plot issues.
Pro Tip 2/3Overemphasis Error
Using the idiom hints someone is making a mistake by concentrating too much on details rather than understanding the main point. 
They argued over the color of the banner and couldn't see the forest for the trees - the event's success mattered more.
Pro Tip 3/3Neutral Context
The phrase is neutral and can be used in both positive and negative contexts, depending on the speaker’s perspective. 
He focused so much on font types that he couldn't see the forest for the trees, although his attention to detail was admirable.