I've had readings that seemed wrong at the time, but the actual events were so convoluted that they ultimately proved to be spot-on. I've had readings that were also totally wrong, and to be fair, I suppose I've also given wrong readings. I agree with GryffinSong somewhat, that Tarot for me is mostly an observational and divinatory tool and less a predictive one.
But I think that even when readings are completely off-track, somehow the reading itself fits in the greater scheme of things. For example, a reading tells you you're going to fail at something, which prompts you to try harder to achieve it, and then you do, and succeed, or do not because of that reading, and you fail. Or the reading predicts something will happen, and the foreknowledge causes it to happen or not to happen. The reading itself isn't divorced from "real life," it's a part of it, and the very fact you're doing a reading can alter events.
If nothing else, Tarot forces you to sit down and think about your life in a concentrated way, that has to do something, even if only subtly.