This question, along with it's companion "How does tarot work?" is one that every reader comes up against sooner or later. I never think in terms of absolutes or certainties, more along the lines of "possibilities" shading into "likelihoods" if the picture in the cards is especially clear. I use it in the same way I use astrological predictions: to look for any bias in the evolving pattern of future reality that may encourage or discourage a certain outcome. It's like opening a window and peering in (or out, depending on whether you think the impressions come from within or through some outside agency). In the best sense, you're looking into the querent's subconscious where he or she already knows the answer, just hasn't recognized or acknowledged it yet. (This is in line with the "You make your own reality through subconscious reinforcement" paradigm.) You know you're there when querents experience the "Aha!" moment during a reading. I liken it to "informed opinion" of the SWAG ("scientific wild-ass guess") variety, and don't get all mystical or pious about it. It gives an "edge" on understanding future developments, usually nothing more. I trust my ability to make sense out of the card combinations, I'm a lot more circumspect about insisting on the infallibilty of the advice they give.
It brings to mind the Russian proverb that Ronald Reagan used when negotiating about arms control: "Trust, but verify." The more you can verify the accuracy of your readings, the more your trust will grow. What "feels right" is all well and good, but if it has no manifest expression in the "real world" it's only self-satisfying conjecture. In that empirical sense, I wonder how many of us ever really get there. "For entertainment purposes only," anyone?
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