There was a discussion elsewhere or Curse by departed forefathers on pithru shapam.. Some people where raising a question as to why the departed fathers and grandfathers and their great grandfathers who all love their children so much would curse them just for not offering some rice morself or gingely seeds and water in time..
In my view the curse does not come from the Pithrus, but the controller of the order and truth in life.. the Supreme being himself..
I give below my own post there
We have to look at it in a diiferent way. The moment we are born to our parents we become debtors to our pithrus.
The debt account is not managed by our affectionate fathers who will definitely condone and pardon everything.
But the account is handled by the eternal keeper of righteousness rtam and satyam.
Call him Shankara or Narayana or Dharmaraja or Varuna or Chitragupta.
The liability is arising from drawal of credit from universal dharma.
Pithrus have no control over the balance, deposits or withdrawals.
When there is default there can be interest penalty and even prosecution.
This can add up to papam and shaapam from the controller of rtm..Narayana or others..
it is called pitrusapam not because it is the curse of pitrus but because the cause of the curse is failure on our part in respect of our duties to pitrus.
Note that if I injure my mother she may pardon me but the law of the land will not.
Such punishments are given by the State not on the basis of complaint by affected party