Answer

1. It is hard for me to answer that. Someone who restrains himself because the sages said there is danger in it is observing Jewish law (in his view). The sages who prohibited it also genuinely thought so, and therefore they did not violate a prohibition. Good-luck practices with no source are indeed close to being prohibited.
2. Same as above.
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Questioner:
The early sages who said that there is a bad sign in a person’s selling his first piece of land—didn’t they violate “do not practice divination”? If we say that they really believed it, then we could also say that someone who sees a black cat really believes it is a bad sign, and on that day will refrain, say, from making business deals. In that way, we would basically uproot the prohibition of “do not practice divination.”
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Rabbi:
The same difficulty can be raised about all the signs mentioned in the Talmud. I truly do not know. Someone who really thinks this way, or believes he has a reasonable basis for it, does not transgress. It is like using alternative medicine: even though it is probably nonsense, that does not make it prohibited, because people think it works. True, according to Maimonides there is a prohibition against being foolish, but it is hard to infer from that that someone who is innocently foolish transgresses a prohibition, even a prohibition under duress. The prohibition applies where you follow something that you understand has no real basis. There are such situations, though admittedly they are rare. Maimonides held that if a wise man like himself tells you that all these things are nonsense, then of course you should accept his words and you too understand that. That is naïve, of course.
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Questioner:
In Yoreh De’ah, section 179, the Shulchan Arukh mentions various examples of soothsaying and divination, some of which are permitted and some prohibited. I do not understand the difference between those that are permitted and those that are not—what is the criterion for prohibition? According to what you said, if a person truly believes in some superstitious belief connected to divination or soothsaying, then there is no prohibition here. If so, suppose I believe that if I spend money on Saturday night, it will be a bad sign for the rest of the week financially—why would I be forbidden to act in accordance with that belief?
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Rabbi:
Who says you are forbidden? At least assuming there is some reasonable basis for that belief and it is not just delusions. This depends on a dispute among the medieval authorities (Rishonim), because according to Maimonides, something that works is not prohibited, since the basis of the prohibition is being foolish; whereas according to Nachmanides and those aligned with him, there are things that work and are nevertheless prohibited, because one may not resort to powers from the “other side.” Alternative medicine is an excellent example. There are intelligent people who believe in it, but it has no basis whatsoever apart from unrepresentative examples that happened to succeed.
It seems to me that the differences between the actions depend on one of two criteria: a. whether it works or not—that is, whether belief in it is rational or not; b. whether it is a gentile custom or not, since Maimonides ties these prohibitions to gentile practices.