Bradbury wrote “A Sound of Thunder” to remind us that even small events in the past have an impact on the future.
Bradbury enjoyed writing speculative fiction with a social message. Although we are not likely to invent time machines any time soon, this story would definitely serve as a cautionary tale for how our events affect the future.
In the story, a company takes men hunting in the past. They go all the way back to shooting dinosaurs. However, one wrong step can change the future.
"We don't want to change the Future. We don't belong here in the Past. ...Not knowing it, we might kill an important animal, a small bird, a roach, a flower even, thus destroying an important link in a growing species."
Stepping on a butterfly results in a complete change in the future, including the spelling of words and who is elected president.
In our everyday lives, we need to remember the ripple effect, or the "butterfly effect" our actions take. Everything we do, no matter how small, affects someone else. This was Bradbury's moral.