The expression “unable to see the wood for the trees” means: Too beset by petty things to appreciate greatness or grandeur; too wrapped up in details to gain a view of the whole.
In America we are likely to use the plural, “woods,” or possibly to substitute “forest,” but “wood” is the old form and is preferable.
Yes, the saying is at least five hundred years old, and probably a century or two could be added to that, for it must have long been in use to have been recorded in 1546 in John Heywood’s A Dialogue Conteynyng the Nomber in Effect of all the Prouerbes in the Englishe Tongue.
He wrote: “Plentie is no deinte, ye see not your owne ease. I see, ye can not see the wood for trees.”
And a few years later, in 1583, Brian Melbancke, in Philotimus: the Warre Betwixt Nature and Fortune, wrote: “Thou canst not or wilt not see wood for trees.”
The saying has cropped up repeatedly from then to the present, becoming, in fact, more frequent with the passing years.