The butterfly effect is a very serious problem. If a person gets back to the past and does something wrong, and changes the history, it may influence the whole world. For example if a person gets to prehistoric times and kills occasionally a butterfly, then this butterfly won’t pollinate flowers it should pollinate, and this kind of flower will disappear and animals who ate this flower will also die as they have nothing to eat, etc. And this chain may follow till the appearance of people and their evolution. People may change their look and the whole view of the world may change. And there will be no way to correct everything.
