can't see the wood for the trees
To be unable to understand the real situation clearly because you're involvement in it make you loose focus of what is really important
In selling hats at the fair John would not lower the price a single penny . So while he argues that the full price need to be paid to gather as much funds as possible for charity he can't see the wood for the trees, losing sales all day long and collecting much less money than the other that were willing to sell their hat for a little less.