The usual disclaimer about personal opinion based on current beliefs applies. That out of the way, I believe we can’t know the future with any certainty. I feel there are certain events in everyone’s life that are, indeed, written in stone. We can postpone them, or bring them about earlier, but we can’t avoid them. Think of them as teaching lessons. I also believe these things are few in number, with the majority of our future being in constant flux.
I disagree with your statement that psychics use “if nothing changes” as a backdoor escape route. Maybe phony psychics do, but I believe a genuine psychic says this with the realization that the future is dynamic, ever changing, fluid. Turn left at this intersection instead of right, as you had planned, and you change future events. Pick the green one instead of the blue one, and you change future events. Maybe in some cases, they change events minimally, and the predicted future still occurs. In other cases, it sets off a cascade effect, and the future is changed radically.
It seems to me that an expectation of divination always being 100% accurate, is a negation of free will. In other words, you’re a puppet on a string dancing to someone’s tune. No matter what you do, you’re doing what someone has predetermined you will do, if that makes sense. There are of course those who believe this is exactly how things work, but I disagree.
For these reasons, I believe divination is best used as a “probability calculator”, or for guidance, rather than foretelling the future. Another way of looking at it: if the future could be foretold easily, you and I wouldn’t be on this board. We’d be too busy enjoying life on our privately owned tropical islands, being waited on hand and foot by scantily clad young women, all courtesy of our winnings from the big lottery games.