I don't regret
I trust my past self with my whole heart and mind, and I am sure he did what was the right and best thing for him to do at the moment. It may not be the best for me now, but he couldn't know. So I don't blame him, and thus I don't regret anything I did. There's no point in regretting, it leads to nowhere. I surely can learn from, and do differently from what I did in the past, But I do not regret.
Past self has his own troubles and issues, and moods and energy, that present me just doesn't understand. I may not fully understand why past self did something, and I just need to live with that.
Many times I look at other instances of myself as another person. It eases things off by a lot. It helps me accept that I don't have control over some things. Like it's onto someone else that I can't control. It is many times the case.
That's it. I don't have much more to say about this. I just hope I really stick to this rule thingy, because it's not always as easy. But it helps a lot when I do.