Manglik word comes from the planet mars. Manglik dosh are the suffering because of the plant mars in married life of a person. It is believed that the scriptures of Vedic Astrology when Mars is placed in any of the houses 1, 2,4,7,8 or 12, with respect to Lagna or Ascendant, Moon or Venus the person becomes a Manglik. If in case a manglik marries to a non manglik then it can cause the death of the other person or separation in that relationship.
As per my research and experience, every time it is not true that Manglik marrying a non Manglik would lead to death or separation of the other partner. As per my research and study on mangliks and manglik dosh, I have come to know why the above mentioned houses are considered evil for marriage.
It is said that 1st house of the Lagna is 7th from 7th and the 7th is the Lagna for the married partner but the 1st house is makara house which means end of life for the married partner.
Coming to the 2nd house is the 8th house from 7th. This results in threat and difficulties to the partner.
Next is the 4th house devoting domestic environment. It is believed that evil planet occupying 4th or 8th from a bhava spoils the bhava. Hence Mars in 4th house is evil with respect to health and belongings of the people.
Next is the 7th house viewing the legal bonding and health, longevity and quality of the partner. So Mars in that house is not favourable to the above benefits.
Next is the 8th house viewing problems of the native and finance and fortune of the partner.
Last coming to the 12th house signifying the real happiness which an individual have after marriage. Mars position here is not beneficial to happy married life.