The title of the poem suggests its theme. The speaker is traveling through the dark on a lonely mountain road. This is a metaphor for mankind traveling through the dark in life. In the first stanza, the man discovers a dead deer on the road, and he decides to remove it because it is a danger to other drivers since they might have to swerve to miss the deer. When the driver gets out to remove the deer, he realizes it is a pregnant doe who has been recently hit. The man then faces the dilemma of whether he should try to save the baby inside the doe, or whether he should just move the doe and ignore the fawn. A car approaches, and the man can't decide what he should do. He decides to push the doe over the edge of the canyon into the river below because even if he could deliver the fawn, he wouldn't know how to keep it alive. He knows for sure that if he leaves it there, it could definitely cause an accident on a dangerous mountain road.
The theme deals with the decisions we must make in life when the unexpected occurs. The poet is saying how we handle these kinds of things in life represents who we are morally and ethically. If the man had ignored the deer in the road, someone else might have died because the man did nothing. The poet says we shouldn't be bystanders in life; he wants us to be participants. He asks the reader to understand that we must do what is humane and responsible when it comes to the difficult decisions in life. The poem also deals with man's responsibility toward nature, not just toward himself.