Sally-Anne Perks

As to that you may rest comfortably, or in comfortable self-delusion at very least; the visions generated by this potion are not inherently of the immutable future, but of a number of futures or pasts that are all possible somewhere, but not necessarily in the world we live in.

There is Muggle science theory that attempts to explain it, but you do not have the background to appreciate it, so I will forego the lecture. Your fate is not, however, written in stone. No one's is.