Signals and subtlety
People care a lot about the strength with which messages are sent. Subtle messages are often seen as more polite and tactful; explicit messages as rude.
But subtle messages require receivers to already be much in the know. If you are attempting to criticize or police behavior, you will need to be subtle in bringing it up, and yet they must already have some sense of the sins in order to pick up on your subtle message.
How does this work? Information-theoretic differentiation. Recall our pyrite scratch test. The more possible options one needs to distinguish between, the more rigorous and extensive the tests necessary for distinction.
When people walk around already with models of what they might be doing wrong, ways they might be erring or violating norms, it may only take a cough or “ahem” to alter their behavior in the desired direction. But when there isn’t already a “spot” in their brain for being conscientious about a possible error mode, when they didn’t even know they could make that kind of error, that that the behavior could be erroneous in that way, we must be more explicit if we wish them to understand.
(This is also why couples who have been together a while can communicate across the room with eyes and eyebrows: Their models of what’s going on in the room are synchronized enough that specifying and confirming between a relatively small number of understood senses is possible.)