My words are Grant's. He offered no military reason for attacking at Cold Harbor, though he did so at Vicksburg. And his reason for attacking at Vicksburg was 1.) He did not want to fight a siege in the hot summer Southern sun, and 2.) Because his troops believed they could beat the Confederates anywhere, and he did not want them wondering why they were ordered to lay siege to Vicksburg without attempting to assault it.
He regretted both.
It's pretty simple really, but some people want to cover for him, even though he was man enough to admit his regrets.