Here's a metaphor I like to use. Realities and Choices, etc, are like a Game on a CD ROM. All the choices are already there for you to choose, all the possible outcomes that we could make are already on the CD ROM. You just have to choose the path you want to take. As for people telling the future, anybody could say anything about the future, and it would already be a "worldline," there is a worldline for every possibility that could ever exsist.

So in theory if I said, in the future I will turn into a wizard with powers, this is a truth, only I may not choose to create this reality in my worldline. It's like a big contradiction, I am, and have already experienced being a wizard, but I am not choosing to experience myself as one right now.

Now occasionally a person may see or guess into a possible reality, that manifests itself in our world line, then this person could technically be predicting the future, but nothing is written in stone, because any reality can be created, the CD ROM has every possiblity.