To not see the wood for the trees is to be so lost in detail that you miss the whole. He cannot see the wood for the trees.
Americans say forest instead, and the meaning is identical. Anybody who works on one thing for long enough will not see the wood for the trees eventually.
1phrasenot see the wood for the treesTo be so lost in detail that you miss the whole.
“After a month on the accounts he could not see the wood for the trees.”
not see the wood for the trees is a phrase.
Practised in Idioms