Now think back to the regrettable decision you made. Is it fair to hold that decision against yourself which such moral force?
The easiest interpretation (explanation in words) of some thoughts is misleading. For example, affirming an aspect of identity, like "I'm a polite person," has the effect of shaping future behavior, so it's often more of a decision or precommitment than a description, and it's more accurate to call that thought "I should act politely". When seen as an observation of the past, acting on it in the future doesn't follow, but when seen as a decision, it's explicitly about future actions. So if the effect of a thought is (specific) future behavior, it's useful to consider it as referring to future behavior, so that you'd optimize it in that light, take consequences of the thought into account when deciding on how it's going to settle as a judgement. With this change, you'd be able to notice that while it might be true that in the past you've been a polite person, in a given situation "I should act politely" does not follow and could be rejected.
You interpret the thoughts discussed in this post as judging the past, as they talk about the past, but their effect is primarily on your behavior in analogous situations in the future. A better response to these thoughts might be about developing heuristics that improve actions in similar situations, based on analysis of the circumstances of the past mistakes (helpfully committed to memory and emphasized for future reference by emotional responses), rather than assignment of responsibility for the past. It might be more accurate to call such thoughts "Pay attention to this and don't forget to perform post-mortem analysis" and not "This is your regularly scheduled emotional punishment," and act accordingly.
Fair? No; but if there's one class of people I can justifiably be unfair to, it's past versions of me who in any case aren't around to be hurt by it.
For instance, every time I realize that Past Shane has said something that probably made someone else feel bad—unless there's an excellent reason, which as it turns out happens roughly never—I berate him soundly for his stupidity. I think I've actually become kinder and friendlier because I don't want Future Shane to be mad at me.
I seldom have any sympathy for Past Shane; generally he was a dumbass and I don't know what the hell he was thinking. This seems to work for me, maybe because I'm not being hard on myself—only on that other idiot who was running the controls earlier.
Here is an experience that I often have: I'm walking down the street, perfectly content and all of a sudden some memory pops into my stream of consciousness. The memory triggers some past circumstance where I did not act completely admirably. Immediately following this, there is often regret. Regret of the form like: "I should've studied harder for that class", "I should've researched my options better before choosing my college", "I should've asked that girl out", "I shouldn't have been such an asshole to her" and so on. So this is regret which is of the kind: "Well, of course, I should've done X. But I did Y. And now here I am."
This is classic hindsight bias. Looking back into the past, it seems clear what my course of action should've been. But it wasn't at all that clear in the past.
So, I've come up with a technique to attenuate this kind of hindsight-bias driven regret.
First of all, tune in to your current experience. What is it like to be here, right here and right now, doing the things you're doing. Start zooming out: think about the future and what you're going to be doing tomorrow, next week, next month, next year, 5 years later. Is it at all clear what choices you should make? Sure, you have some hints: take care of your health, save money, maybe work harder at your job. But nothing very specific. Tune in to the difficulties of carrying out even definitely good things. You told yourself that you'd definitely go running today, but you didn't. In first-person mode, it is really hard to know what do, to know how to do it and to actually do it.
Now, think back to the person you were in the past, when you made the choices that you're regretting. Try to imagine the particular place and time when you made that choice. Try to feel into what it was like. Try to color in the details: the ambient lighting of the room, the clothes you and others were wearing, the sounds and the smells. Try to feel into what was going on in your mind. Usually it turns out that you were confused and pulled in many different directions and, all said and done, you had to make a choice and you made one.
Now realize that back then you were facing exactly the kinds of uncertainties and confusions you are feeling now. In the first-person view there are no certainties; there are only half-baked ideas, hunches, gut feelings, mish-mash theories floating in your head, fragments of things you read and heard in different places.
Now think back to the regrettable decision you made. Is it fair to hold that decision against yourself which such moral force?