Pitra Dosha is a Topic which many modernized well-educated astrologers most of them actually less Educated, look at with disdain and contempt. They say that this is used for squeezing money from the Clients. I do not think that any Good Astrologer would ever earn his Fees by putting Fear in the minds of his Clients; rather he is supposed to allay their Fears.
A Brief visiting into the reasoning for the Causes of this Dosha: -
1) Not doing the Tarpan, and Shradhas, Annual and otherwise properly.
People either don’t have time, or do not know about this, or do not care about this, or do it carelessly, or get it done by their servants for formality sake.
2) Insult of the Ancestors or forgetting them.
This is one prime reason for temporary misfortunes and unfortunate happenings happening from time to time in the family
At time of marriage of some family member, or when some auspicious function is held, if the Ancestors are not invited, or asked for to be taken part of, or not offered their due respects, this Dosha will manifest.
3) Acting against ones Kul Dharma
Suppose you are a Brahmin and start drinking Alcohol or eating Non-veg, then this Dosha will manifest and you will become eligible to receive a curse from your Ancestors. Same for the other Varnas and Kulas.
4) Killing a Cow or a Snake.
Cow is considered to be a “Mother” since she gives Milk. And one is not supposed to kill his Mother. A Snake is already a small form of SheshNaga and also most of the ancestors who have died in Alpa Ayu or untimely deaths get a Snake Yoni, therefore killing these are considered as Great Sins.
5) Not worshipping Kul-Devata or Kuldevi.
Who is the Kul-Devata or the Kuldevi? They are the same Gods who have protected our Ancestors when they were alive. So when the ancestors see you now no more remembering these Spiritual entities and ignoring them, one invites this curse. Even for those who do NOT know who their Kuldevi is, we have an injunction through which these can be worshipped. In all Maanglik karyas in the family they must be remembered and made a Part of.
6) Answering Call of nature in some Pond, River or in the Sea.
We as Hindus must know that the Sea (Samudra) is known as “Bhraaman devta). In any case Water is the substance with which we offer tarpan to our Ancestors. Spoiling clear water by urinating on it carries a great sin thus. (One should not even urinate in a secluded place under any Tree.)
7) Apkarmas done in a Temple or Teertha Sthal.
These are places where one visits to wash off his Sins, and not to add further. Native must avoid doing these here.
8) Having sex on Amavasya (New Moon).
Does one have Sex in front of his parents? No. On Days like new Moon, the dead Ancestors get a chance to visit the family and see into their affairs. If they have to watch you copulating, then the consequences can be well understood.
9) Physical Sexual relationships with Guru-Stri, Guru Patni or a prostitute.
A “Guru” is the Trinity of Brahma, Vishnu and Mahesh. That said. No Kul allows or sanctions the men of their family to visit prostitutes. So if one does “Maryaada Bhang” of his Kul, then naturally he no more remains “Maryada Purshottam” but becomes worse than Ravana.
This is NOT Sanctioned. One prevents a Soul from attaining a Human Body when he indulges in this act. A Human Body is what even the Devatas in the heavens desire for. So when one indulges in this, he is going against nature and has to suffer for this gruesome Act. (Nature will not stop you from doing abortion, raping someone, or murdering someone coz God has given you free Will. But it will take its course of Action. Because in Law of Nature every Effect has a Cause, and Vice versa).
How the above Curses manifest in one’s Birth Chart (Janma Kundli) and how to locate them, and also what are the remedial measures, is a subject matter which is best reckoned by an Able Astrologer and not just by a common man.