An obvious implication of this post is that if someone tells you that you "should have known better", then rather than getting upset and instantly trying to defend yourself, it might be a better idea to calmly ask the person "How should I have known better?".

Possible answers include:

1) "using this simple and/or obvious method that I recommend as a general strategy" 2) "using this not simple and/or not obvious method that I didn't think of until just now" 3) "I don't know" 4) "how dare you ask that!"

The first two of those answers are useful information about how to do things, and thus valuable. You can then perform a quick cost/benefit analysis to check if the cost of implementing the suggested strategy outweighs the cost of risking another instance of whatever mistake you just made.

The third is a result of a successful use of the technique, generally. The speaker now realizes that maybe you didn't have any way to know better, and so maybe it would be inappropriate to blame you for whatever went wrong.

The fourth is a sign that the person you're talking to is probably someone you would be better off not interacting with if you can help it (and thus is useful information). There are ways of dealing with that kind of person, but they involve social skills that not everyone has.

Another obvious implication of this post is, if you're about to tell someone else that they "should have known better", then it might be a good idea to take a moment to think how they should have known better.

The same 4 possible answers apply here.

Again, in cases 1 and 2, you might want to take a moment to perform a quick cost/benefit analysis to check if the cost of implementing the suggested strategy outweighs the cost of risking another instance of whatever mistake the person just made. If your proposed solution makes sense as a general strategy, then you can tell the person so, and recommend that they implement it. If your proposed solution doesn't make sense as a general strategy, then you can admit this, and admit that you don't really blame the person for whatever went wrong. Or you can let the other person do this analysis themself.

In case 3, you can admit that you don't know, and admit that you don't blame the person for whatever went wrong. Or you can just not tell the person that you think they "should have known better", skipping this whole conversation.

In case 4, you obviously need to take a moment to calm down until you can give one of the other answers.

A philosophy professor recently told me that one of the few things philosophers agree on is that there can't be a moral obligation to do the impossible-- ought implies can

Some dispute this; there is a concept of (bad) "moral luck".

To some people, it's completely obvious that torture is a bad thing and doesn't work, and to others, it's completely obvious that getting important information for one's own side is an emergency, people can't lie if they're suffering enough, and people on the other side don't deserve careful treatment.

This example seems a bit odd, as half of it is about a factual matter...

I generally unpack "X should have known better than to believe Y" as a way of burying the assertions that X believed Y and that Y is obviously false into the "tail" (that is, the de-emphasized part) of a claim, with a status-challenge tacked onto the front as bait.

This is a common rhetorical technique when people want to direct skeptical attention away from an assertion; the hope is that others will respond to the bait (in this case, the status challenge) and let the assertion go by unchallenged. For example, the hope is that a discussion will ensue about whether or not it's really true that X should have known better, which implicitly concedes that X believed Y and Y is false.

It tends to be a warning sign for me... when someone uses a construction like that, I try to remember to pay particular attention to whatever the bait is distracting me from. Did X really believe Y? Is Y really false? Has the speaker actually given me any reason to believe those things?

This is similar to the urban self-defense principle that when something really dramatic happens down the block, that's a very good time to take a step back and look carefully around you for potential threats.

Related post on consequentialist analysis of blame-assignment:

• Diseased thinking: dissolving questions about disease

I think that "X should have known better" can be legitimately true, but the implications and level of accusation/nurture needs to be calibrated in radically different ways when X is, for example: a child, an adult idiot, a college professor, or the leader of a large organization.

The idea of a teachable moment seems to be largely about noticing when someone has a problem that was caused by a more abstract process failure and intervening in the moment when they care deeply about the object level issue to help them solve that and also to notice the process failure. This happens all the time with children.

I think part of why the issue gets complicated is that competence of this sort seems like one of the obvious criteria that should be used to select a leader. Even though humans are not automatically strategic, a competent leader in their 40's or 50's should, by that age, have already cultivated strategic planning abilities that include proactively seeking out information related to the domain for which they have official responsibility, figuring it out, and applying it as appropriate.

If an organization experiences a major failure, people who don't really understand all the details of what it would have taken to prevent can still infer that the existing leadership didn't have the ability prevent it for some reason and to forestall a demand for regime change the leadership needs to explain why no alternative leaders could have handled the issue any better. This could be a legitimate point: the best poker player in the world will still lose some hands.

In our daily life, if someone says to us that "tragedy T happened because you didn't check S first" that can be an act of helpful teaching or a social power grab or both. If someone is predisposed to see that sort of thing as a power grab, or is inordinately fond of autonomy, they might end up get a bit defensive when someone tries to teach them something. This might be adaptive, or not, depending on other factors.

A philosophy professor recently told me that one of the few things philosophers agree on is that there can't be a moral obligation to do the impossible

Oh dear, Eliezer won't like this...

You make some good points, but I still say this guy should have known better. (Warning: Violent video.)

This seems to me like yet another case where a label is sometimes valid and sometimes invalid, and we have to use our judgements in applying it, and our judgements aren't very good.

The overlap between what people believe is moral and what they believe is effective is probably worth another essay

Yes, this occurs for so many people over all sorts of beliefs, when there's no good reason for their to be much of a correlation at all (I suppose some form of divine command theory theist could argue that God has made the world so that correct morals also give practically the best results.)

Upvoted for content. Though it strikes me as slightly redundant (gut feeling), I think that it covers some important points. Organizationally, I would change your thesis so that it better reflected what the rest of the post was going to be about -- the post struck me as rambling a little too much.

Thoughts:

Since I cannot prove my value system on an absolute scale, I sometimes restrict use of the word 'should' to technical applications where there's no ambiguity about the objective. For moral arguments, I like to use 'I think that you would want to' as a replacement for 'You should' -- it seems more intellectually honest, less opaque, and less provocative.

I interpret 'should have known better' as a data-sparse, unnecessarily antagonistic comment -- it doesn't tell the listener much about how they should revise their updating system and risks causing negative emotions toward the speaker. I also think that it causes future action to be more pain motivated because 'avoiding harsh correction' may become one of the listener's motivations for improving.