"That is because they're idiotic," says Kaylo. "It extrapolates the future. The problem is, what I'm likely to do feeds into the future. So if I'm in the wrong frame of mind - it's not even an intentional component like normal spells - when I cast it, then my decisions if I get whatever result will feed into it and I get noise. For the spell to be useful I have to sit on the sidelines enough for it to get a result that doesn't factor me in, but not so far that I can't interrupt if it turns out giving you a potion will be a disaster. And you will too, since I guess you'll be able to both see what results I get and affect the processes that would lead to them."