Position of moon in horoscope is a key. It's position can make a big difference in predicition. Eeven at the time of match making, the analysis is based on the position of moon. In our classics some yoga has been mentioned which are highly misfortunate.These are called "Vish Kanya Yoga". The word "vish" is called poison and "Kanya" means girl. Even the male born under such combinations has the same effect.
The nakshatras Ashlesha, Vishakha, Jyeshta, and Moola. are trouble causing.
a)One born under Ashlesha first quarter brings death to one's mother-in-law.
b)Those born under Vishakha last quarter could cause death to married partner's younger brother.
c)If born under Jyeshta first quarter, there is danger to partner's elder brother.
d)Those born under Moola first quarter may indicate early death of father-in-law.
The above effects are too general.One parameter can not result in formation of yoga. There must be some supportive combination
1)The birth on the 12th Tithi, Shatabhisha nakshatra and on a Sunday.
2)Birth on Tuesday when the Tithi is 7th and the nakshatra happens to be Vishakha.
3)The 2nd Tithi on a Saturday when the Moon is in Ashlesha.
4)Birth on Sunday when the Moon is in Bharani nakshatra.
5)Birth on Monday with the Moon in Chitra.
6)On Tuesday, Moola nakshatra.
7)Combination of Wednesday and Dhanishta.
8)Combination of Thursday and Jyeshta.
9)Combination Friday and Purvashada.
10)Combination Saturday and Revati.
The above combination needs micro analysis.But in modern times it is often seen that the boy and girls matches their charts own with the help of computer on guna basis only which is very risky