Sometimes you can't see the wood for the trees.
You are maybe too close to a situation and just can't make sense of it.
As a dyslexic I often experience this especially when it comes to working with ornate fonts. Somebody recently sent me something in Times New Roman and it looked like a forest of fast growing thorns.
Here's a great video which shows some of the effects people can have. It's a bit extreme but you get the idea of what it's like when you can't see the wood for the trees.