In astrology, why is the 8th house often seen as a difficult placement for planets, and how does Jupiter specifically suffer from this?

According to the Cosmic Man (Kaalpurush) chart, the Scorpio (Vrishchik) sign falls in the eighth house, and according to human anatomy, the eighth house signifies the private parts. That means the eighth house is considered mysterious and complex. The eighth house indicates knowledge of subjects like calamities, sudden occurrences, hidden things, occult knowledge, research, life span, spirituality, etc. This is why the eighth house is considered more challenging compared to other houses; planets situated here often cannot express their energy and power easily.

Generally, the environment of the eighth house does not suit any planet that well, yet it proves troublesome for benefic planets like Jupiter (Guru), Mercury (Budha), and Venus (Shukra). And if the sign over there is not compatible with that planet, then a contradiction is observed during the periods of those respective benefic planets.

The planet Jupiter is the significator planet of expansion, knowledge, morality, education, religion, progeny, marriage, the fifth house, etc. Instead of learning towards bad paths here, Jupiter in the eighth house can enhance a person's cognitive senses towards subjects like occult knowledge, tantra-mantra, astrology, etc. The eighth house belongs to secrecy, transformation, and uncertainty, because of which Jupiter's journey of knowledge and Jupiter's significations face some degree of constraint here, and its energy does not manifest openly; the wealth of knowledge is not obtained easily, it has to be learned through experience. On the other hand, looking from a spiritual perspective, because the eighth house is the second house within the salvation trine (Moksha Trikon), Jupiter here can bring unimaginable growth and success in a person's life from a spiritual standpoint.