I think if you look too closely at *how* something works, it stops working. Scientists seem to think that observed scien tific phenomena work differently under observation to when they are not under observation. Someone concentrating on muscular movements at the gym or during dance who thinks about their body very often finds their skill deserting them until they forget about it and go back into automatic mode. And how many of us actually *think* about braking, accelerating, turning or changing gear in a car? - we don't, it's all automated through the limbic system, and when it isn't yet (as an inexperienced driver) and we are thinking about what we do, we are not so good at it.
Personally, I disagree with this, and I think that Trzes pointed out why quite nicely. Thinking about something doesn't make that thing stop working. If it did, engineers would be terrible drivers, doctors would suffer from chronically bad health, and physicists would find themselves no longer bound by the law of gravity. In my opinion, stopping to ask "why?" is always helpful; it's led us to a world that's not flat, to a human body more complex than just a sack of humours, and to the thousands of personal conveniences that make life in the modern world so much more pleasant than life in Europe in the Middle Ages.
I don't buy this idea that Tarot works, and that's it. If it works, that's great, but why stop there? Why not at least make an attempt to understand the mechanism behind it, the source of this mysterious "working"? Even if a reader comes up with a theory and it's wrong, implementing that theory will allow her to form more specific ideas about her use of Tarot, and to implement Tarot as a tool more effectively.
Personally, I actually don't agree with the assertion that Tarot "works" in the sense that it can supernaturally provide a reader with knowledge that she didn't previously have. I remain skeptical on that point. I do think that Tarot can stimulate thought on the part of the querent, and can directly affect an individual's choices, but I don't see any magical mechanism behind it. If the Eight of Wands comes up in a reading, then the querent reflects on recent creative projects, maybe decides to push a little further with them, and ends up pursuing the arts as a career. In that sense, Tarot "works" because a reading has affected the querent's actions in the real world. But as to why the Eight of Wands came up, and not another card? I know I differ from most of the rest of the forum on this point, but I personally have never found reason to believe that there's a guiding mechanism behind it beyond simple chance.