Answer:
His carelessness.
Explanation:
Ray Bradbury's short story "A Sound of Thunder" is a science fictional story set in 2055 AD. The ability of the time travel in the story also made it all the more intriguing, taking the characters and the story back t the age of dinosaurs.
The main character Mr. Eckels is a man who seemed to be not only arrogant but proud and selfish. He only thinks of his personal success and wanted whatever possible to be done to get his hands on a dinosaur. But once the time machine took them for the hunt, he couldn't shoot anything. He was so impressed and in awe of the size of the dinosaur that he was unable to shoot it. The tour guide Travis bade him return to the machine but he went the wrong way which led to the animal seeing him and thus lead to the worst disaster of the story. When they returned back to the present age, he not only saw that he still had mud and a dead butterfly in his boots, but also that Deutscher had been elected president. His careless actions in the hunt had changed the whole system of the present age.
