It has a connection to the planet Mars. Mars is a symbol for ego, temperament, self-worth, and conflict. It's a hostile planet. You may be aggressive and violent if certain sections of your birth chart (kundali) are put there; this could perhaps cause marital problems. Your horoscope will tell you if you're a Manglik or not. The date, year, hour, and location of your birth are used to create your horoscope.
Those who have the Ujjain Mangal Dosh Puja feel that the Manglik influence significantly distorts the compatibility between the potential bride and groom. There is a notion that the Manglik should first do a ritual known as a Kumbh vivah in order to alleviate the negative effects of a single-Manglik marriage.