I think the theme of the story is to follow directions. In the story, when everyone time travels, they are not supposed to stray from the metal path because if they do, it will cause a butterfly effect. Eckels did not listen to the instructor and ran off of the path, killing a butterfly while doing so. He changes the future and is killed by Travis. Because he did not follow directions, he faced consequences. If he followed directions like he should have, nothing bad would have happened.