The speaker asks a guilty question: how many friends has he lost because he was too absorbed in the natural world? Waiting for winter shadows, watching clouds reflected in a forest pool, following a slug along a fungus-covered log, he has given his attention to small wonders and let human connections wither. The slug is described with real delight, especially its eyes retracting "all the way into its head," so the poem shows exactly what has pulled him away.
The mood mixes regret with stubborn devotion. He admits the cost, even saying he has learned to be "merciless" with himself, which he links to editing. Yet he doesn't take it back. He settles in the mountain hollow, where no walk is ever the same twice. The closing image of a birch growing over a rotting hemlock stump suggests that his rootedness is a kind of life built on loss. The stump decays, but its hollow shape remains inside the tree, much as the lost friendships may remain in him.