[Epistemic status: This is really a draft that I should edit into something presentable. This is probably obvious to lots of us, but whatever, I’m rederiving social normality from the ground up. Draft.]
Common, fragile, concepts
There are a number of common, simple, concepts that, when examined closely, appear to break down, or at least be much more complicated than they seemed at first.
For instance, the idea of “I” or who “myself” is. This concept is a standard part of most people’s navigation of the world, but if we turn a philosophical eye to it, we run into all kinds of confusions: am “I” the same person at the person named Eli Tyre who was in high school 10 years ago? What about the person who was resting “20” minutes ago? What about the transporter problem?
This concept is a workhorse of day-to-day living and deciding, but it is shockingly fragile, as evidenced by those edge cases.
Nuance vs. Pragmatism
One might be more or less satisfied with a given level of conceptual clarity around a topic. I might have a pragmatist attitude that ignores or papers over the finicky fragility of concepts, and doesn’t bother much with the nuances of meaning.
Or I might be a stickler for the nuance: really caring, about having clarity around these details, making sure that I understand what I’m talking about.
The same person might have a different attitude in different contexts: I’m a pragmatist when I need to get the milk, and a philosopher when I need to think about cryonics. (But in practice, it also seems like there is a fairly stable trait which represents how much of a stickler someone is.)
Being a stickler for nuance is often detrimental to cooperation. As a case in point, suppose that my neighbor’s cat is sick. The cat really needs to be taken to the vet, but my neighbor is has a crucial business meeting with an important client and if he misses it he’ll be fired. In desperation, my neighbor asks me if I can take his cat to the vet. (He doesn’t know me very well but there’s no one else around and he’s desperate.)
With panic for his beloved pet in his eyes, he asks me, “can I trust you?”
Supposes my response is, “Well, what do you mean by trust? Are you attempting to assess my level of competence? Or are you wanting to know the degree to which our values are aligned? In fact, it’s not even clear if “trust” makes sense outside of a social context which punishes defectors…”
For most normal people, this response sets off all kinds of alarm bells. His was is a simple question, but I seem unwilling to answer. My neighbor now has good reason to think that he can’t trust me: One reason why I would be desiring so much legalistic clarity about what “trust” means, is because I’m intending to hold to the letter of my agreements, but not the spirit, to screw him over while claiming that the precise definition shields me from reproach. Or maybe it means I am something-like-autistic, and I just legitimately don’t understand the concept of trust. In either case, he should be much more reluctant to trust me with his cat.
In this circumstance, it seems like the correct thing to do is put aside nuance, and give the simple answer: “Yes. You can trust me.” The shared social context has a very limited number of buckets (possibly only “yes” and “no”) and in fact the most correct thing to say is “yes” (presuming you in fact will take care of his cat). It is both the case that the available ontology is too simple to support a full answer, and also the case that the response “the available ontology is too simple sot support a full answer” rounds down to “no”, which is not the correct response in this situation.
Being a stickler sabotages cooperation, when that cooperation is shallow.
However, being a stickler is necessary in other contexts where you are aiming for a more robust cooperation.
For instance, if a partner and I are considering getting married, (or maybe considering breaking up) and she asks me “Are you committed to this relationship?”
In this situation, skipping over the nuance of what is meant by “committed” is probably a mistake. It seems pretty likely that the concepts that she and I reference with that word are not exactly overlapping. And the “edge cases” seem pretty likely to be relevant down the line.
For instance, one of us might be meaning “committed” to be a kind of emotional feeling, and the other might be meaning it to be a measure of resources (of time, attention, life) that you are promising to invest.
Or one of you might feel that “committed” means that you’ll want to spend most of your time together, if circumstances allow. That’s not part of the other’s concept of committed, and in fact, they will feel defensive of their own autonomy when “circumstances allow”, and their partner expects them to spend most of their time together.
Not having clarity about what exactly you’re agreeing to, promising, or signaling to the other, seems like it is undermining the ability for robust cooperation.
Unless you insist on this conceptual nuance, there isn’t actually clarity about the nature of the relationship, and neither party can in full confidence rely on it. (In practice, it maybe more likely that two partners don’t notice this conceptual mismatch, and so do put their weight on the relationship, only to be burned later.)
If I want to have a robust, long standing marriage with my partner, it seems like we really do need to do enough philosophy to be clear about, and have common knowledge about, our shared concepts. 
I posit that this is generally true: Insistence on conceptual nuance can undermine cooperation, particularly in “shallow” interactions. But a failure to insist on conceptual nuance can also undermine cooperation, in other contexts.
 Although, maybe in some contexts you don’t need to do the philosophy because tradition does this work for you. If culture mandates a very specific set of requirements around marriage, or business dealings, or what have you, you can safely operate on the assumption that your concepts and the other person’s concepts are sufficiently similar for all practical considerations? The cultural transmission is high bandwidth enough that you do both have (practically) the same concepts?
I don’t know.
Addendum: 2019-11-16: I just realized that this dynamic is exactly(?) isomorphic to the valley of bad rationality, but at the interpersonal, instead of the personal level