"Tarot cards never lie." Is this true?

Some people think so, and I’m not justified in believing it. For example, the chance of one card of the tarot that tells you that you are going to die is 1/40 because if I'm correct, the tarot hand has 40 cards. The chance that one of those cards will say that you are going to have a pleasant and calm life, therefore, is also 1/40. As a result you have a very good reason to begin writing your testament for believing that you are going to die, or a very good reason to start packing for a better life. 

Eventually, if this knowledge has some certainty than of course, the preposition that the tarot cards works will have some certainty. But, what kind of certainty? I know that the tarot cards are all designed in such a way that any card that is thrown will make you think that you are going to die or that you will have a pleasant life,but the human brain is not designed for good reason to doubt a preposition, but for some reason, is designed to find some sort of justification. In fact when people need some sort of justification, or just because they have heard a testimony that the cards do actually predict the future, the less background of information to justify a preposition, the less conflict with the preposition and the more reason there is not to doubt it. However, if you put a question mark after Tarot; if we have good reason for believing it to be false, it will not justify the preposition to be true. Even if all our sensory evidence indicates that it is. I have a good reason to doubt a reading if it conflicts with the exactitude of the prediction that I have reasons to believe. Like Descartes said once, “When it is not in our power to determine what is true, we ought to follow what is most probable”.

I don't believe in the tarot because I do can figure out for myself what it is more probable to happen in the future of my actions than a reading of cards that has algorithms designed to propose your future. But, in fact your own future is determined by what choices you make. Yes, you can have a pleasant life after all, but even if the reading says that you are going to be rich, I can't say that the possibility of you becoming rich is implausible in fact it could happen in 3 ways. (1) you win the lottery , (2) you choose wisely or (3) you are lucky enough to that you have choose wisely.

The tarot randomly will tell you the future that you want to hear, but will never tell you how your future is going to be.

Astrology. What would you do to show them the error of their ways? (My thoughts)

Try to find a good reason to make them think that astrology is wrong, better reasons, better prepositions, astronomy.

The more  likely it is they will start thinking scientifically the better. Some people who believe in astrology believe that to know about planets is the ability to predict the people's personality, future, and to have no doubt of what kind of life this person will have depending in its zodiac sign. I would find good reasons to make them doubt about what astrology propose, than, I think they cannot have a good reason to believe in astrology. But how? and why take their believes away like a father taking the candy from his beloved kid?

In the first question of the how, I would try to explain the laws of physics and demonstrate that gravity is stronger on an apple being hold by your hand than the gravity of a planet affecting on you. I would try to demonstrate through out perception, introspection, memory, and reason that the constellations in the sky are no entirely still, that stars move like planets and that they have nothing to do with your personality; I would try to show them how mathematics works to explain the physics behind nature so they can have reasons to find the scientific method more interesting by learning more scientific background.

Just like they were the very same Babylonians who thought and reasoned the misconception of the position of planets having an effect on you. I would try to make them think that hepatoscopy is not the way to know the future just by explaining that the liver is an organ, that you only have one and is not meant to sacrifice it for the gods to get your future revealed by the their made up gods.  Teaching them real science would make the astrology believers, them who have no reason, to not doubt what's disclosed to them through perception, introspection, memory, or reason than what they are justified in believing through astrology.