One should be regretful. When we say we should regret, it’s more of allowing oneself to be regretful. It’s not a program like getting up early, exercising between 7.00 am to 7.30 am, performing puja between 7.30 am and 8.00 am and then sitting for a session of regretting between 7.35 am and 7.50 am. It’s not a question of us ‘being’ remorseful, it happens. We think about our mistakes and to have wronged troubles us.  And so even though we may not suffer actual losses because of it but its mere remembrance unsettles us.
Paschataap: Paschat means after and taap means pain
It’s said that one should not do this. It’s also said one should not exercise ego. But no one tells to accept its existence and understand it.

And so we must understand Paschataap. On the path of success, we don’t recall the good events or the received appreciation. What we remember is our mistakes and it hurts because Paschataap or being regretful is a self correcting system. He who recalls only appreciations may get embroiled in it and hence there are the memories of mistakes. They make us equipped and conducive to move forward.

It pains because we accept that a mistake has happened. If we allow it to pain, then its intensity and frequency reduces. If we suppress it, then its intensity may increase.

‘I am such a donkey. How did I behave at that time?’ When we reprimand ourselves like that it cleanses our personality.