The change in people's lives can sometimes effect another's.

You know how in movies where the main character will get there fortune told that one day they will die by a specific cause? Such as in this one story I had read, a man goes to a fortune teller to have his fortune told. He is told that his cause of death will be his favorite horse. So naturally the man sends the horse to another farm so it wont kill him. Weeks later, the horse become sick at the farm and dies. Seeing as he still loves the horse, he stops by and asks to see whats left of the horse. At this point, there is almost nothing left except some bones and such, but also a large skull. As he leans down to touch the skull, a rattlesnake which had made his home inside the skull bites him and he dies soon after.

Either way, the cause of the death was still because of his horse.

Now here's the twist! What if the man never went to see the teller? He wouldn't have sent his horse away, it probably wouldn't have gotten sick, died, and the rattlesnake wouldn't of bit him. He probably would have gone on with his life, happy as can be. But instead, the fortune made him paranoid and caused a chain reaction which caused him to die.

The point here is, knowing what could happen in the future could change what the future is. Change cannot always be controlled to how you want it to be.