A pattern, not a curse
A dosha is just a pattern in a chart that old books said to watch. It means "handle with care". It does not mean "doomed". About one in three charts has Mangal dosha by the common rule. If it were a disaster, a third of the world would be living one.
The tradition agrees. Almost every dosha comes with a long list of ways it is cancelled (bhanga) or made softer. Popular stories skip that list.
Mangal dosha
This happens when Mars sits in the 1st, 2nd, 4th, 7th, 8th, or 12th house from the lagna or the Moon. It is read as heat in relationships. Strong feeling, friction, a strong will.
Many things cancel it or make it softer. Mars in its own sign. Both partners having it. Age, in many traditions. Several other placements too. Context is everything.
Kaal Sarp dosha
This is said to form when all seven classical grahas sit between Rahu and Ketu. It is read as a life with strong karmic themes. Intense chapters, and rewards that come late but are real.
One thing to know: the oldest books do not mention it at all. It is a later idea. Many respected astrologers give it little weight, or none.
How to hold a dosha
If a reading says you have a dosha, three questions matter more than the word itself. Is it really formed, by the strict rule? Is it cancelled or softened somewhere else in the chart? And what does it ask of you day to day - patience with a partner, care with anger, respect for timing?
Anyone who starts with fear, or with a price for removing it, is not doing astrology. The old answer to a dosha is first to know, then to act. And remedies were always meant to be gentle.