How does one avoid regret? If the person is a psychopath, it’s easy, regret may not even arise no matter how vile the behavior.
But for most human beings, the path to no regrets is paved with the gleaming white marble stones of doing the right thing.
Other than the natural human aversion to admitting errors, it’s fairly easy to express regret for actions taken or not, long after the time when that choice would have made a difference is past.