I loved Elven's ruminations too and they got me to thinking...
We are turning around the issues of "what is the future?" and "what is predestination?" and 'what is divination?" and "is there such a thing?" and "if so, how do you ever know?" and "do tarot cards really do anything?", "does tarot 'work'?" and "what does 'working' mean?"
On the lowest, most unexamined level, tarot cards do what they are supposed to do... we throw them, we pull them out of the stack, we take note of the probable meanings, and wait and see if something happens in the next few days or weeks that we can relate back to the cards. I got the Three of Swords, and three days later I had a sleepless night. Voilà! Presto! Instant prediction of the future with one hundred percent accuracy!!!
Elven points out that everyone involved in future events has a piece in the puzzle. But, you see, that's just it... .. philosophically it's impossible: if you can predict the future at all, it would be a future that actually will happen, not a future that could have happened... but didn't. Such is not the future.
But the future does not exist. It never did. I like Elven's analogy of everyone's future being a house under construction. I like to call it a vector of force that we set in motion. "This is the house you've constructed and the direction you're going in..." is a reading of the present, and the past.
To divination I say "uncle'. The future, the real future, exists in hindsight. Except for genetic pre-pramming -- which dictates we will fight for food, shelter, mates and territory, grow old and require reading glasses -- "Predestination" is a construct of revisiting the past.
Therefore, the very thought-provoking question brought up by Umbrae and by Mary, "is tarot predictive or something far deeper?" - can never be satisfactorily answered. The mind cannot understand itself... Unless there are other parallel universes we can pop into on occasion... like the underside of the mobius strip...
If prediction were all there was to tarot, many of us would not bother turning the cards over and over, asking how the the flapping of the tarot butterfly wings connected to the monsoon in India.
But let's ask the Thoth what it would like to contribute to this discussion, shall we??? I've gotten the Princess of Disks. Oh I love how her winding horns and woven hair, the tangled branches and splayed roots of denuded trees behind her, and the gnarled twisting of her infinite cape -- like a thousand tangled wires, connecting everything to everything... I love how she points with her gleaming staff into the depths of the underworld, mining for precious gems with her thoughts -- as if thoughts could skewer to the center of the earth.
Methinks best of all, the tarot is a reflective mirror for exploration of psychic depths.