In Vedic astrology, the planet Mercury represents intelligence, communication, and analytical ability. It is said to have a strong influence on the way individuals express themselves and interact with others. When Mercury is placed in 8th house for lagna Sagittarius, it is considered to be in an enemy sign state. In this placement, Mercury becomes the lord of houses such as 7th and 10th house which can affect how it takes care of its own houses.
One of the main astrological predictions for this placement is that it could lead to financial instability due to unexpected expenses or losses. The presence of Mercury in the eighth house could make individuals prone to impulsive decisions when it comes to investments, leading to losses. Henceforth, one must apply caution when making investments and ensure making informed decisions based on financial analysis.
With respect to personal relationships, this placement suggests that those with this combination may have trouble expressing their emotions or connecting with others emotionally. Individuals may struggle with emotional intimacy or building trust in relationships which might result in developing misunderstandings among partners if ignored for long.
On a positive note, however, Mercury’s natural ability as a karaka for 4th and 10th houses can help these individuals achieve success in their professional lives through good communication skills, sharp analytical ability thereby becoming an excellent problem solver at work.
The aspect of Mercury on the second house would give rise to intelligent speech and enable a person's wealth-building prospects through the power of speech/communication. Nevertheless, they shouldn't overlook domestic affairs importance while striving forward professionally. This aspect specifically implies earning money through hedged investments or risk-taking involving strategized market projections.
Furthermore having expertise in profound areas like occult sciences such as astrology that rely heavily on one’s intuitive abilities will be more benefited by native having mercury placed in eighth house because being lord of seventh house helps them earn name fame through counseling clients who are seeking spiritual remedies meanwhile they can supplement their income from client consultation.
In conclusion, the placement of Mercury in 8th house for lagna Sagittarius is not considered the most auspicious placement. But having a deep understanding of Vedic astrology allows us to realize that every planetary combination has some good and bad effects that depend on various other factors. The above predictions are generic and could differ on a case-by-case basis, taking into account other aspects like the positioning of other planets or the effects of ongoing dashas/bhuktis in one's life. Therefore, it is imperative to have a detailed analysis of one's birth chart by an experienced astrologer before arriving at any conclusion.