Every one of us has some or big regret about something or the other. As long as it is just a disappointment about something one has done, or failed to do, it not an issue. When deep or persistent regret becomes remorse leading to guilt or shame, it is a problem and it needs to be addressed.
A regret can take the form of blaming oneself or blaming someone else. Understanding and coming to terms with the fact that no amount of regret can undo what has already been done goes a long way in coming to terms with the situation. After the battle of Kurukshetra, Yudhisthira blamed himself for the disaster. He was counselled by the grandsire Bhishma about the inevitability of the war. The solution was to go beyond, accept the responsibility of kingship, and give good governance.
Even as the blind king Dhritarashtra blamed the Pandavas for the killing of all his sons in the battle, Vidura and Sannatkumara advise him to stop the blame game. He was told to take the responsibility for his own acts of omission in averting the war.
The remedy was to accept the Pandavas as his children and live in peace. Regrets come in many hues and are not insurmountable. Some forms of remorse can be mitigated by penance. Emperor Ashoka embraced Buddhism and gave up violence after the horror of the battle of Kalinga. Japan as a nation did not try to get back into the arms race after the Second World War.
Closer home, Gandhi suggested adoption of the children who had been orphaned in the riots of partition by the perpetrators of the violence. The penance was bringing up the child in its own religion. More common regrets are often a result of social and emotional narratives. These narratives keep playing on the mind and often take the form of disgruntlement.
Regretting a career choice is often the result of seeing the choice in terms options that may not have been available. Regretting the choice of partner, especially if the matter is not serious enough to warrant a break up, could just be an over romantic exaggeration. The more serious remorse of having made the wrong choice of intervention in the care of a loved one may require therapy. Becoming aware of the narratives and changing them helps to put things in perspective. Constant regret can become a habit which is negative and unbearable to oneself and loved ones.