Good practitioners of things like tarot tend to be rather decent empirical psychologists, who are acutely aware of how to pick up cues conveyed by the client, and say things which will be accepted. Watch one work, at something like a street fair sometime. Even though, in that setting, most of the clients are simply doing it for a lark, you can appreciate how a good card reader operates. Couple that to the fact that the more serious client desparately WANTS to believe, and the card meanings are arranged (as are many “divinatory” tools) to seem insightful when in fact they are just making random hits.
Hell, something like tarot might actually bring somebody some kind of understanding of a problem - not because the cards have any magical properties, but simply because they are a focusing agent, causing the person to reflect on the problem in a new way. Many spiritual practices work this way - it’s not that the mechanism has any validity, but that belief in the mechanism or adherence to the discipline associated with it can gain results. In this sense, prayer, tarot, tea-leaf reading, I-Ching, etc., can all be said to “work”.
On another level, read up on the tarot sometime. I find the symbolism fascinating, and running rather contrary to what you might expect of Medieval Europe.