What epiphany happens in a sound of thunder short story?

The main epiphany in the short story "A Sound of Thunder" by Ray Bradbury is about the fragility and delicate balance of the past and the future. The protagonist, Eckels, travels back in time to hunt a prehistoric dinosaur but accidentally steps on a small butterfly, unintentionally changing the course of history. This incident illustrates how even small actions in the past can have profound and unpredictable consequences in the future, highlighting the delicate balance between the cause and effect of time travel and the importance of preserving the past.