Strangers are a potential threat. So when a stranger comes up to you and initiates a conversation, there's some reason to be on your guard.
This is combined with basic etiquette. If someone makes a small request, it is considered rude to refuse. The problem here is that creepy weird dangerous strangers can take advantage of this fact by making a small request, which then makes you feel obligated to comply. So now a complete stranger, who may be dangerous, has ensnared you. You're now doing something that he asked, instead of something that you want to do. And he can keep you dancing to his tune by making more small requests. So if you follow the rules of etiquette, a complete stranger, possibly dangerous, can monopolize you for a significant length of time.
I see this happen all the time with telemarketers. The phone will ring. Somebody will answer it. Then they'll be at the phone for a long time, maybe half a minute maybe a couple of minutes. And it turns out that it was a telemarketer, and the reason the person stayed at the phone for a long time was that he just couldn't think of a polite way to end the conversation. You go ahead and try it. If you try to disengage, the telemarketer has a scripted response ready which cancels your attempt.
For my part, I'm not trapped by telemarketers. But I simply hang up. I say "no thanks", and the telemarketer goes on to the corresponding point in his script, and I simply hang up on him while he's in the middle of a sentence. That's rude. But I do it, because there are no personal repercussions for me in doing it.
Being rude to a stranger face to face is not as easy to do. If you're rude to someone, they might get angry, and one thing might lead to another. So it's easy to hang up on telemarketers (for me, but importantly, not for everyone) but not so easy to "hang up" on a stranger right in front of you. For this reason, being approached by a stranger represents a more serious potential problem, a social trap that may be more difficult to get out of.
So what do you do? There are plenty of ways to initiate a conversation. One is to be already with somebody. If you're not alone, if you already have a conversational partner, and if you're deep in conversation with them, then you are obviously less in need of company, so the possibility that you might try to trap a stranger into a conversation is correspondingly reduced. Another method is to get the other person to initiate the exchange.
The thing to do with telemarketers, I have learned, is not to immediately hang up.
You just let them get to what they want to sell you, then say, loudly but politely and without a pause for them to butt in, something like "Let me stop you there, [name], I'm afraid I'm not interested, but thank you very much for calling." If they don't back down, THEN summarily hang up.
I prefer this to simply hanging up because doing the latter always makes me feel bad for several minutes afterward for having been rude to somebody who is, after all, trying to make a living.
I am beginning to suspect that it is surprisingly common for intelligent, competent adults to somehow make it through the world for a few decades while missing some ordinary skill, like mailing a physical letter, folding a fitted sheet, depositing a check, or reading a bus schedule. Since these tasks are often presented atomically - or, worse, embedded implicitly into other instructions - and it is often possible to get around the need for them, this ignorance is not self-correcting. One can Google "how to deposit a check" and similar phrases, but the sorts of instructions that crop up are often misleading, rely on entangled and potentially similarly-deficient knowledge to be understandable, or are not so much instructions as they are tips and tricks and warnings for people who already know the basic procedure. Asking other people is more effective because they can respond to requests for clarification (and physically pointing at stuff is useful too), but embarrassing, since lacking these skills as an adult is stigmatized. (They are rarely even considered skills by people who have had them for a while.)
This seems like a bad situation. And - if I am correct and gaps like these are common - then it is something of a collective action problem to handle gap-filling without undue social drama. Supposedly, we're good at collective action problems, us rationalists, right? So I propose a thread for the purpose here, with the stipulation that all replies to gap announcements are to be constructive attempts at conveying the relevant procedural knowledge. No asking "how did you manage to be X years old without knowing that?" - if the gap-haver wishes to volunteer the information, that is fine, but asking is to be considered poor form.
(And yes, I have one. It's this: how in the world do people go about the supposedly atomic action of investing in the stock market? Here I am, sitting at my computer, and suppose I want a share of Apple - there isn't a button that says "Buy Our Stock" on their website. There goes my one idea. Where do I go and what do I do there?)