Every failure of human endeavor can be traced to a Dosha (defect) in the horoscope. There are some Doshas that are very well known, and there are some that are not well known. Whatever these Doshas are in the Kundali, they definitely influence the horoscope.
A Kundli is necessarily formed by the misdeeds and misfortunes one has experienced in previous births. Knowing these Doshas ahead of time can solve many of one's problems.
People have done weird things in the name of rituals to achieve their goals. In various rituals, they try to appease the God associated with the planet that is hindering their progress. Despite the common misconception, Vedic karma is not about appeasing deities, but simply about correcting our deeds or karmas through various Doshas and Yogas in the horoscope.
A planet sitting in an enemy sign, a planet associated with a negative planet, a planet aspected by a negative planet, a planet or a group of planets in a negative house, a planet in a negative nakshatra, and a planet in a negative house in any of the Shodashvarga are primary reasons for the Doshas formation in a Kundli.
he general effect of Manglik Dosha depends on its placement in the horoscope and can be any of the points mentioned as under :
This work should be left to an experienced astrologer. So you need an experienced astrologer to figure out all the Dosha in a horoscope. These astrologers can also work out the strength of these Dosha and then guide you more towards karma correction than mindless remedial measures.