I think a life without regrets in how we treat others is for the enlightened or the narcissists - and I do not think I have ever met someone enlightened.
Great thoughtful phrase indeed. Then, I must be one enlightened or a plain narcissist. Because I certainly have no remorse or regrets whatsoever as for how I treated everyone alive in my surroundings.
However, I think the great little secret for this, is simply having acted all your life guided by the deepest love and authenticity of those who know themselves fully in all their human dimension.